In pictures: The human cost of modern warfare as Russian invasion sets Ukraine ablaze

Ukrainian forces ‘repelling attacks’ as fight for Kyiv goes on

Russian forces have advanced towards major Ukrainian cities, forcing people to flee in their thousands to neighbouring countries.

Big explosions have been heard in Kyiv, Kharkiv, and Odessa as world leaders condemned the invasion that could potentially lead to mass casualties and topple Ukraine’s democratically elected government, while threatening the post-Cold War balance.

Ukraine’s president Volodymyr Zelensky declared martial law after Russian troops began their offensive and called on citizens to take up arms against their invaders.

Mr Zelensky said Ukraine’s armed forces were successfully fighting back against Russian troops and had “derailed” Moscow’s plan to take Kyiv and install a puppet government.

“We have withstood and are successfully repelling enemy attacks. The fighting goes on,” Mr Zelensky said.

The Ukrainian preisdent declined an offer from the US to be evacuated as he wanted to support efforts in Kyiv, according to a US intelligence source.

Three children were among the 198 Ukrainians killed since Russia’s invasion began, the Ukraine government said.

Ukrainian soldiers look for and collect unexploded shells after fighting with Russian troops in Kyiv on Saturday (AFP/Getty)

Ukrainian soldiers take positions outside a military facility as two cars burn, in a street in Kyiv (AP)

A flat block damaged by recent shelling in Kyiv on Saturday (Reuters)

Ukrainian service members look for and collect unexploded shells after a fighting with Russian raiding group in the Ukrainian capital of Kyiv on 26 February 2022 (AFP/Getty)

A Ukrainian man with a child kisses his wife as Ukrainians cross the border from Ukraine to Poland (AFP/Getty)

Firefighters work by a high-rise apartment block which was hit by recent shelling in Kyiv on 26 February 2022 (AFP/Getty)

People approach bags of toys for children fleeing from Ukraine who arrive in Slovakia on 26 February 2022 (Reuters)

People wait for a bus to Poland at a bus station Lviv on Saturday (AFP/Getty)

Ukrainian service members are seen at the site of a fighting with Russian raiding group in the Ukrainian capital of Kyiv (AFP/Getty)

Anna Semyuk, 33, hugs her children, after a stranger took them across the border and kept them safe while fleeing from Ukraine and arriving in Hungary (Reuters)

Ukrainian service members look for and collect unexploded shells after a fighting with Russian raiding group in the Ukrainian capital of Kyiv on 26 February 2022 (AFP/Getty)

A Polish Border Guard carries a child near the border crossing between Poland and Ukraine on 26 February 2022 (Reuters)

Surveillance footage shows a missile hitting a residential building in Kyiv, Ukraine on 26 February 2022 (Reuters)

Natali Sevriukova reacts as she stands next to her house following a rocket attack in the city of Kyiv, Ukraine, Friday 25 February 2022 (AP)

Firefighters inspect the damage at a building following a rocket attack on the city of Kyiv (Ukrainian Police Department Press Service via AP)

Servicemen of the Ukrainian National Guard take positions in central Kyiv (Reuters)

A man inspects the damage at a building following a rocket attack on the city of Kyiv (AP)

Black smoke rises from a military airport in Chuguyev near Kharkiv on 24 February 2022 (AFP via Getty Images)

A child sits on a swing in front of a damaged residential building (Reuters)

A wounded woman stands outside a hospital after the bombing of the eastern Ukraine town of Chuguiv on 24 February 2022 (AFP via Getty Images)

People look at the damage following a rocket attack the city of Kyiv (AP)

Ukrainian servicemen get ready to repel an attack in Ukraine’s Lugansk region on 24 February 2022 (AFP via Getty Images)

A Ukrainian firefighter walks between at fragments of a downed aircraft (AP)

Rescuers help a local resident after shelling in the town of Starobilsk (Press service of the Ukrainian State Emergency Service via Reuters)

People gather in an air raid shelter in Kyiv (Reuters)

This photograph taken on 24 February 2022 shows an Ukrainian infantry combat vehicle BMP-2 standing guard on the outskirts of Kyiv (AFP via Getty Images)

Rescuers help a local resident after shelling in the town of Starobilsk (Press service of the Ukrainian State Emergency Service via Reuters)

A room of a damaged residential building is seen, after Russia launched a massive military operation against Ukraine, in Kyiv (Reuters)

Firefighters work at a damaged residential building at Koshytsa Street, a suburb of the Ukrainian capital Kyiv (AFP via Getty Images)

Firefighters work at a damaged residential building at Koshytsa Street, a suburb of the Ukrainian capital Kyiv, where a military shell allegedly hit, on 25 February 2022 (AFP via Getty Images)

People take shelter at a building basement while the sirens sound announcing new attacks in the city of Kyiv, Ukraine (AP)

Firefighters work at the site of a damaged residential building, after Russia launched a massive military operation against Ukraine (Ukrainian Ministry of Emergencies via Reuters TV)

A view of a damaged residential building, after Russia launched a massive military operation against Ukraine, in Kyiv, Ukraine, 25 February 2022 (Ukrainian Ministry of Emergencies via Reuters TV)

A man kisses a boy who just crossed the border with his relatives on 24 February 2022 (Getty Images)

Smoke rises from the territory of the Ukrainian Defence Ministry's unit in Kyiv (Reuters)

A man from neighboring Ukraine, kisses his daughter at a train station that was turned into an accommodation center in Przemysl, Poland (AP)

People walk on the street after crossing the Slovak-Ukrainian Internation crossing border on 24 February 2022 (Getty Images)

A couple hugs in Central Kiev as bombs rain down in the capital (AFP via Getty Images)

Black smoke rises from a military airport in Chuguyev near Kharkiv on 24 February 2022 (AFP via Getty Images)

(Anadolu Agency via Getty Images)

An injured man stands by a vehicle of an Emergency unit to receive medical assistance after bombings on the eastern Ukraine town of Chuguiv on 24 February 2022, as Russian armed forces are trying to invade Ukraine from several directions (AFP via Getty Images)

View shows the aftermath of shelling in Kharkiv, Ukraine 24 February 2022 (Reuters)

A group picture shows American evacuees on a bus as they prepare to leave Kyiv (Project Dynamo via Reuters)

People walk past the body of a relative outside a destroyed building after bombings on the eastern Ukraine town of Chuguiv on 24 February 2022 (AFP via Getty Images)

Ukrainian military track burns at an air defence base in the aftermath of an apparent Russian strike in Mariupol, Ukraine, Thursday, 24 February 2022 (AP)

A man sits outside his destroyed building after bombings on the eastern Ukraine town of Chuguiv on 24 February 2022 (AFP via Getty Images)

The body of a rocket stuck in a flat after recent shelling on the northern outskirts of Kharkiv on 24 February 2022 (AFP via Getty Images)

The body of a rocket stuck in a flat after recent shelling on the northern outskirts of Kharkiv on 24 February 2022 (AFP via Getty Images)

Resident stands in an apartment that received a shelling in Kharkiv (Reuters)

People wait for buses at a bus station as they attempt to evacuate the city on 24 February 2022 in Kyiv (Getty Images)

People wait for buses at a bus station as they attempt to evacuate the city on 24 February2022 in Kyiv, Ukraine. (Getty Images)

A rocket case lies buried into a road after recent shelling in Kharkiv, Ukraine 24 February 2022 (Reuters)

Smoke and flame rise near a military building after an apparent Russian strike in Kyiv, Ukraine, Thursday, 24 February 2022 (AP)

Firefighters work on a fire on a building after bombings on the eastern Ukraine town of Chuguiv on February 24, 2022, as Russian armed forces are trying to invade Ukraine from several directions, using rocket systems and helicopters to attack Ukrainian position in the south, the border guard service said (AFP via Getty Images)

Ukrainian military vehicles move past Independence square in central Kyiv on 24 February 2022 (AFP via Getty Images)

Ukrainian army soldier sits in truck, after Putin authorised military operation, in Kharkiv region (Reuters)

Damaged radar arrays and other equipment is seen at Ukrainian military facility outside Mariupol, Ukraine (AP)

Damaged radar arrays and other equipment is seen at Ukrainian military facility outside Mariupol, Ukraine (AP)

Damaged radar arrays and other equipment is seen at Ukrainian military facility outside Mariupol, Ukraine, Thursday, 24 February 2022 (AP)

Smoke rise from an air defense base in the aftermath of an apparent Russian strike in Mariupol, Ukraine, Thursday, 24 February 2022 (AP)

Military vehicles drive along a street, after Russian President Vladimir Putin authorized a military operation in eastern Ukraine, in the town of Armyansk (Reuters)

Tanks move into the city, after Russian President Vladimir Putin authorized a military operation in eastern Ukraine, in Mariupol, 24 February 2022 (Reuters)

People board a bus as they attempt to evacuate the city on 24 February 2022 in Kyiv, Ukraine (Getty Images)

A child stands at the border crossing between Poland and Ukraine, after Russian President Vladimir Putin authorized a military operation in eastern Ukraine (Reuters)

A woman reacts as she waits for a train trying to leave Kyiv, Ukraine, Thursday (AP)

People shelter at the Kyiv train station, Ukraine, Thursday, 24 February 2022 (AP)

An American woman cries after crossing the border and fleeing the violence in Ukraine, in Medyka, Poland, 24 February 2022 (Reuters)

A woman stands in a street as black smoke rises from a military airport in Chuguyev near Kharkiv (AFP via Getty Images)

A man walks on a street as black smoke rises from a military airport in Chuguyev near Kharkiv on 24 February (AFP via Getty Images)

Vladimir Putin announced what he called the invasion during a televised address on Thursday morning, saying the attack was intended to protect civilians in eastern Ukraine – a false claim the US had predicted would be made the pretext for an invasion.

Mr Putin accused the US and its allies of ignoring Russia‘s demands to prevent Ukraine from joining Nato and for security guarantees. He also claimed that Russia does not intend to occupy Ukraine but will move to “demilitarise” it and bring those who committed crimes to justice.

Alexander (right), reassures his son as his family takes refuge in a metro station in Kiev in the morning of 24 February (AFP via Getty Images)

People hug as a woman with a suitcase uses her smartphone outside a metro station in Kiev in the morning of 24 February (AFP via Getty Images)

People, some carrying bags, sit in a metro in Kiev in the morning of 24 February (AFP via Getty Images)

People line up to withdraw money at a cash dispenser in Kiev in the morning of 24 February (AFP via Getty Images)

Traffic jams are seen as people leave the city of Kiev (AP)

Police and security personnel inspect the remains of a shell in a street in Kiev (AFP via Getty Images)

Russia’s military said it was targeting Ukrainian air bases and other military structures, not the populated areas, but troops have since made advances on several cities.

Ukraine responded with an attack on a Russian air base in Millerovo, according to Russian media.

A woman with a child and a dog walks at a metro station in Kiev early on 24 February (AFP via Getty Images)

Local residents follow the news on their mobile devices in a bomb shelter on 24 February in Kiev, Ukraine (Getty Images)

US president Joe Biden denounced Russia’s action as an “unprovoked and unjustified attack”, declaring “the world will hold Russia accountable”.

The US has announced harsh sanctions targeting Russia’s banks and influential individuals. The UK has made personal sanctions against Mr Putin and his defnece secretary, Sergey Lavrov, among other measures.

The European Union agreed the “strongest, the harshest package” of sanctions on Friday.

A senior Russian official has warned that Moscow could react to sanctions by opting out of the last remaining nuclear arms pact and freezing Western assets.

A handout photo made available by the Latvian Defence Ministry shows the first 40 soldiers of the 173rd U.S. Army Airborne Brigade after stepping off a military plane in Latvia, 24 February 2022 (EPA)

A handout photo made available by the Latvian Defence Ministry shows the first 40 soldiers of the 173rd U.S. Army Airborne Brigade after stepping off a military plane in Latvia, 24 February 2022 (EPA)

Around 120,00 refugees have fled Ukraine to neighbouring Poland, Moldova, Hungary, Romania and Slovakia, the UN said. The largest numbers were arriving in Poland, where 2 million Ukrainians have already settled to work in recent years. At the Medyka border crossing, the line of vehicles waiting to enter Poland stretched 9 miles into Ukraine. Poland declared its border open to fleeing Ukrainians, as did Hungary. “We will help everyone,” the Polish Border Agency said. “We will not leave anyone without help.”