KIEV, Aug. 18 - Dozens of people, including women and children, were killed as they fled fighting in eastern Ukraine on Monday when their convoy of buses was hit by rocket fire, a military spokesman said.

Ukraine accused pro-Russian rebels of targeting the convoy, which it said was bearing white flags when it was hit near the eastern city of Luhansk. The separatists denied responsibility for the attack and one rebel leader suggested the incident might never have taken place.

"The rebels were expecting the convoy and destroyed it entirely," military spokesman Andriy Lysenko told journalists, Reuters reported. "We haven't been able to count the number of victims ... dozens (were killed)."

The convoy had been in an area of fierce fighting between government forces and the separatists when it came under fire from rebel Grad and mortar launchers, the spokesmen said.

"A powerful artillery strike hit a refugee convoy near the area of Khryashchuvatye and Novosvitlivka. 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.

Describing the attack as a "bloody crime," Lysenko said: "A lot of people have been killed including women and children. The number of the dead is being established."

A rebel leader denied any civilian convoy had been struck, challenging the Kiev authorities to produce evidence.

"As far as I understand, there was no column of refugees in Luhansk region that fell under fire. We ... did not shoot any convoys (of refugees) with Grads and moreover we did not shoot with any Grads from Russia," said Alexander Zakharchenko, the main rebel leader in Donetsk.

In Kiev, a military spokesman, asked about visual evidence of the attack, said there was video footage on the Internet, although this could not immediately be traced.

"My press officer was on the spot. There is no telephone link with him now but he was there and confirmed that the convoy was travelling under white flags and the terrorists were warned that a convoy with peaceful citizens would be passing," Oleksiy Dmytrashkivsky told Reuters.

He said the press officer had confirmed that many bodies of victims were burned beyond recognition.

The Kiev military reported new successes overnight, building on a weekend breakthrough when troops raised the national flag in Luhansk, a city held by pro-Russian separatists since fighting began in April.

Troops blockaded or recaptured rebel-held positions after international talks in Berlin failed to reach agreement on a ceasefire. Nine soldiers were killed.

Western sanctions against Moscow have failed to stem what NATO says is a steady supply of military equipment and men sent from Russia to help the rebels. Russia denies sending support, saying the rebels have seized equipment from the Ukrainians.

President Petro Poroshenko called on his top security advisers on Monday to address claims by the rebels to have received new stocks of heavy Russian military equipment and 1,200 trained Russian fighters.

Referring to the heavy loss in life among government forces, he said: "Today we need to regroup our forces to defend our territory and continue offensive actions by the army." (rt/ez)