Fighting flared between Ukrainian and pro-Moscow separatist forces, both sides reported on Sunday, further straining a unilateral ceasefire declared by Ukraine as Russian President Vladimir Putin pressed Kiev to talk to the rebels.
Putin and Ukrainian President Petro Poroshenko, at separate ceremonies marking the anniversary of Nazi Germany's invasion of the Soviet Union, both stressed the need to bring peace to Ukraine's rebellious east.
The seven-day ceasefire came under pressure almost as soon at it began on Friday night, with the government accusing the separatists of attacking its military bases and posts on the Russian border. The violence continued for a second night into Sunday.
“Unfortunately, what we are seeing ... tells us that the fighting is still going on and last night we saw some active use of artillery from the Ukrainian side,” Putin said after laying flowers at the Tomb of the Unknown Soldier in Moscow.
He said it was not clear whether artillery was used by the Ukrainian army or the “so-called paramilitary of the right-wing forces” supporting the government. He appeared to attach no blame to separatist forces.
Poroshenko wants Putin's unqualified backing for a 15-point peace plan he announced on Friday, before meetings with the European Union in the coming week. These will include the signing on June 27 of an association agreement with the bloc which includes a free trade deal.
In his comments published on the Kremlin website, Putin repeated his support for the ceasefire and peace plan in only general terms.
In pictures: The Ukraine crisis
In pictures: The Ukraine crisis
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Ukrainian soldiers from the 'Azov' battalion guard their base in Mariupol, Donetsk
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Children were transferred from orphanages in Donetsk and Makeyevka to escape the fighting between the Ukrainian army and pro-Russian separatists
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Ukrainian servicemen captured by pro-Russian separatists sit on the ground as they are assigned to clean a street in Snizhne in the Donetsk region
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A view inside the Youth Culture Centre destroyed by pro-Russian separatists in Donetsk
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A woman holds a portrait of her dead son as she speaks during a rally in front of Ukrainian President Petro Poroshenko's office in Kiev
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A boy ascends the stairs of a bomb shelter after the shelling in the Petrovskiy district in Donetsk
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A medic looks at thirty coffins prepared for the funerals of pro-Russian rebels killed during heavy fighting at Donetsk airport, outside a Donetsk morgue
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Relatives mourn near the coffin of Mark Zverev, a taxi driver shot dead during clashes at the Donetsk airport between Ukrainian troops and the pro-Russian rebels, during his funeral in the village of Grabari on the outskirts of Donetsk
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Medical workers carry a wounded pro-Russian militant on a stretcher after armed clashes occured between pro-Russian gunmen and Ukrainian troops in Slavyansk
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A member of a newly-formed pro-Russian armed group called the Russian Orthodox Army mans a barricade near Donetsk airport
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Black smoke rises from a shot down Ukrainian Army helicopter outside Slovyansk
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A woman is overcome with emotion as she looks at blood stains and damage around a wrecked truck of supporters of the self-proclaimed 'Donetsk People's Republic' on road leading to the Donetsk International Airport
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A local man looks at damage near a wrecked truck of supporters of the self-proclaimed 'Donetsk People's Republic' on road leading to the Donetsk International Airport
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A bloodstained icon of Jesus is seen among blood soaked shattered glass atop a wrecked truck near the Donetsk airport
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A family member attends a funeral for Olga Prokhorenko (60) who was killed by shrapnel after Ukrainian government forces shelled their location, during the funeral in Slovyansk
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A woman reacts after seeing the lifeless body of a man killed by shrapnel following a shelling from Ukrainian government forces in Slovyansk
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Pro-Russian militants take position on the roof of the international airport of the eastern Ukrainian city of Donetsk
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A woman embraces a pro-Russian separatist from the "East" battalion during a rally in the eastern city of Donetsk
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A Ukrainian helicopter Mi-24 gunship fires its cannons against rebels at the main terminal building of Donetsk international airport
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A pro-Russian gunman changes his position near the airport, outside Donetsk
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A pro-Russian gunman aims his weapon near the airport, outside Donetsk. Ukraine's military launched air strikes against separatists who had taken over the airport in the eastern capital of Donetsk in what appeared to be the most visible operation of the Ukrainian troops since they started a crackdown on insurgents
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Pro-Russians ride on a truck in Donetsk. A convoy of an armored personnel carrier and seven trucks carrying several hundred heavily armed men drove through central Donetsk and gunmen got out of the trucks, stood to attention and gave shots in the air in jubilation as a crowd of several thousand supporters cheered them and chanted: "Heroes!"
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An elderly woman leans against the chest of a pro-Russian gunman in Lenin square in Donetsk
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Pro-Russian militants guard a psychiatric hospital after shell explosions during the fighting between pro-Russian militants and the Ukrainian army, in Semyonovka village, outside Slavyansk
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Ukrainian troops stand guard at a checkpoint on the road near the eastern city of Izum, Donetsk
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Members of the Democratic Alliance party take part in a performance in front of the French embassy in Kiev. Protesters set up a pool with the blood of animals and models of warships in a protest against French plans for the sale of two Mistral helicopter carriers to the Russian Navy
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A man carries a portrait of pro-Russian activist Vadim Hudich, who was killed in a shooting incident at the head of a funeral procession in the eastern Ukranian town of Krasnoarmeisk
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A voter is seen inside a voting booth at a polling station during the referendum on the status of Donetsk region in the eastern Ukrainian city of Donetsk
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Members of a local election commission sort ballots as they start counting votes of referendum on the status of Luhansk region in Luhansk
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Members of a local election commission empty a ballot box as they start counting votes of the referendum on the status of Donetsk region in Donetsk
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Members of a local election commission empty ballot boxes as they start counting votes after a referendum, at a polling station in Lugansk
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Local residents watch as others give first aid to a man who was shot in the leg by Ukranian militia in the village of Krasnoarmisk. Eyewitness said that Ukranian militia tried to stop the referendum voters briefly taking the City Hall of Krasnoarmisk, where unarmed pro-Russian supporters were gathering. Reportedly the Ukranian militia came out out the building and started shooting at the people, killing at least one man and leaving at least two others injured
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Members of a local election commission count votes after a referendum organized by the so-called Donetsk People's Republic members at a polling station in Donetsk
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Voters visit a polling station to take part in the referendum on the status of Donetsk
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An Armoured Personnel Carrier (APC) with a Russian flag drives through the center of Slaviansk during the day of referendum organized by the so-called Donetsk People's Republic members in Slavyansk
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A statue of Lenin is placed in front of a pro-Russian barricade on the outskirts of the eastern Ukrainian town of Slavyansk
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A feamle veteran (C) sings during 'Victory Day' celebrations in Donetsk
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People stand near the burning Mariupol police station
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Ukrainian soldiers stand guard beside an armoured personnel carrier at a checkpoint in Mariupol. Ukrainian forces seized the rebel-held city hall in the eastern port city of Mariupol, driving out pro-Russian activists, then withdrew, making no attempt to hold onto the building
“We need to ensure that all fighting is stopped,” he said. “Ultimately the political process is the most important. It is important that this ceasefire lead to dialogue between all opposing sides in order to find compromises acceptable for all.”
Poroshenko told US Vice President Joe Biden during a phone call on Sunday that Russian separatists continue to attack Ukrainian forces, including with artillery, despite the ceasefire, the White House said.
“The vice president reiterated that the United States was working closely with its G-7 partners to prepare further economic sanctions against Russia if Moscow did not take actions ... to stop the flow of arms and militants across the border and use its influence to publicly call on the separatists to lay down their arms,” the White House added.
The insurgency in the largely Russian-speaking east erupted in April after street protests in the capital Kiev toppled the Moscow-backed leader Viktor Yanukovich. Russia subsequently annexed Ukraine's Crimean peninsula and the West has accused Russia of supporting the insurgency.
French President Francois Hollande and German Chancellor Angela Merkel urged Putin by telephone on Sunday to work for the resumption of talks to end the conflict, Hollande's office said.
The two leaders “reiterated the importance of ensuring full control of the Russia-Ukraine border to prevent the infiltration of gunmen and military equipment”, the statement said.
In Kiev, Poroshenko stressed the need for dialogue, saying his plan “was specifically put together to ensure peace, the laying down of weapons and to establish, through talks, a single united state”, news agency Interfax Ukraine quoted him as saying.
Ukraine's state border service reported further rebel attacks on its posts in Luhansk region on Sunday, while a separatist spokesman said Ukrainian forces were firing mortars at a village near the Russian frontier.
In Donetsk region, which like Luhansk has declared itself a “people's republic”, rebels reported a morning shootout with Ukrainian troops in Siversk, north of the city of Donetsk.