Refugees travelling in a convoy in eastern Ukraine have reportedly been killed by a missile strike as they tried to escape fierce fighting between government forces and rebels.
There has been no independent confirmation of the attack, which the Ukrainian military said killed “many people”, including women and children on Monday.
The column of vehicles was reportedly travelling through the rebel stronghold of Luhansk, which has seen fierce fighting between separatists and government forces, when it was hit.
"The force of the blow on the convoy was so strong that people were burned alive in the vehicles - they weren't able to get themselves out," military spokesman Anatoly Proshin told Ukrainian news channel 112.ua.
Around 500 people a day have been fleeing Luhansk, which has been battered by months of fighting between rebels and Ukrainian forces and left almost entirely without water and electricity for more than two weeks.
A Ukrainian military spokesman, Andriy Lysenko, claimed “militants” armed by Russia fired at a the convoy with mortars and Grad rockets.
“Many people have been killed, including women and children,” he said.
But pro-Russian rebels were quick to deny that they were behind the strike, saying they did not have the military capability for such an attack.
Andrei Purgin, deputy Prime Minister of the self-styled Donetsk People's Republic, said: “The Ukrainians themselves have bombed the road constantly with airplanes and Grads.
“It seems they've now killed more civilians like they've been doing for months now. We don't have the ability to send Grads into that territory.”
Spokespeople for the Ukrainian military said the attack happened near the areas of Khryashchuvatye and Novosvitlivka and the death toll had not been counted.
A rebel news outlet had previously reported heavy artillery fire between government forces and separatists near where the buses had been travelling.
Ukraine crisis: Russian 'aid' convoy
Ukraine crisis: Russian 'aid' convoy
1/11 Ukraine crisis
Drivers of the first trucks of the Russian aid convoy parked in the city of Luhansk on 22 August
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An employee inspects the contents of a truck with Russian humanitarian aid in Mariupol, Ukraine on 22 August 2014
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The convoy nearing the border before it parked at a camp in Russia
4/11 Ukraine crisis
Russian convoy carrying humanitarian aid for residents in rebel eastern Ukrainian regions moving along a road in the city of Voronezh, about 530 km from Moscow, Russia
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An Ukrainian border guard checks passing cars at a checkpoint of Pletnyovka, Kharkiv region on Ukraine-Russia border, where Russian humanitarian convoy is to cross the border
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Ukrainian border guards stand at the Ukrainian-Russian border crossing
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Trucks of a Russian convoy carrying humanitarian aid for Ukraine are parked at the military air base outside Voronezh
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Drivers of a Russian convoy of trucks carrying humanitarian aid for Ukraine take a rest on a side of a road near the city of Yelets
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An Ukrainian soldier stands guard at a checkpoint of Pletnyovka, Kharkiv region on Ukraine-Russia border, where Russian humanitarian convoy is to cross the border
10/11 Ukraine crisis
A Russian convoy carrying humanitarian aid for residents in rebel eastern Ukrainian regions moves along a road about 50 km from Voronezh, Russia, 14 August 2014. The convoy continues to advance through Russian territory after a one-day stop in Voronezh in full coordination with and under the aegis of the Red Cross, according to Russian authorities
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The Russian convoy carrying humanitarian aid in the Voronezh region of Russia en route to Ukraine
Civilians have been suffering chronic food and water shortages and power cuts caused by sustained shelling by Ukrainian forces.
The UN’s human rights office said the number of people killed in the conflict has risen dramatically in recent weeks, with at least 2,086 people killed and 4,953 wounded by 13 August.
Video: Fighting continues in Ukraine
A Russian aid mission is expected to enter the country “in the near future” after inspections by Red Cross officials.
The charity is waiting for guarantees from separatists that the convoy will not be attacked or stopped as it passes into rebel territory.
Additional reporting by Reuters