MOSCOW (Reuters) - More than 100 Russian soldiers were killed in eastern Ukraine in a single battle this month while helping pro-Russian separatists fight Ukrainian troops, two members of the Russian presidential human rights council said on Thursday, citing accounts from eyewitnesses and relatives of the dead.

Ella Polyakova and Sergei Krivenko, both members of the council - an advisory body with no legal powers and an uneasy relationship with the Kremlin - said around 300 people were wounded in the same incident on Aug. 13 near the town of Snizhnye, when a column of trucks they were driving, full of ammunition, was hit by a sustained volley of Grad missiles.

“A column of Russian soldiers was attacked by Grad rockets and more than 100 people died. It all happened in the city of Snizhnye in Donetsk province,” Krivenko told Reuters.

Polyakova said she had been given the same figure for the number of Russian soldiers killed.

They said they had spoken to around 10 relatives of the dead and fellow soldiers who witnessed the attack, some of whom had accompanied the bodies back to Russia. Their sources said there was no documentation proving the soldiers had been in Ukraine, and the death certificates were filled out to suggest they had died elsewhere.

“When I talk to the guys who accompanied these coffins of these contract soldiers, they tell me that the order was given orally, there were no forms of documents,” said Polyakova.

If confirmed, the deaths would support assertions by Kiev and its Western allies that Russia is fuelling the conflict in eastern Ukraine by supplying the separatists with both weapons and soldiers.

They pose awkward questions for the Kremlin, which has consistently denied involvement in the conflict. A defence ministry official repeated that denial in strong terms on Thursday.

No one answered the phone when Reuters called a ministry spokesman to ask about the Snizhnye incident.

“The soldiers serving on contract are given an order, and the columns go across Russia and they stop at a camp, as though part of a training exercise, on the border with Ukraine,” said Polyakova.

“They take off all the (identification) numbers or blotch them out, and then cross the border,” she said.

Rebel leader Alexander Zakharchenko said on Thursday that active Russian soldiers were fighting with the rebels against Ukrainian troops but were doing so while on vacation.

Polyakova said not one of the soldiers she or her colleagues had spoken to had filled out a form to go on vacation, standard procedure for contract soldiers.

Krivenko said that around the middle of August they had received complaints from parents of the soldiers that they could not contact their sons.

The pair said they had asked Russia’s Investigative Committee to open a probe into the case.

“We’ve made requests to official bodies, but as of yet we’ve received no answer,” Polyakova said.