Attacks on the humanitarian convoys bringing aid to the besieged city of Aleppo are being carried out by the militia Jabhat al-Nusra, Vitaly Churkin told the UN Security council.
Members of the group, which has previously had claimed with al-Qaeda and attacks Islamic State (Isis) forces, make up the majority of rebel forces in eastern Aleppo, the Russian diplomat said.
"We were near to a resolution in September," Churkin told the emergency meeting of the Security Council, as part of a rebuttal to a scathing report by special envoy Staffan di Mistura accusing Russian and Syrian government forces of using incendiary bombs on civilians.
"Humanitarian aid had been authorised by the government to go through, but then there was an act of provocation by the rebels.
"Each day neighbourhoods with government troops are being attacked with intention of causing as much damage as possible.
"Our American friends for a long time claimed that there were no al-Nusra forces in Aleppo when in fact al-Nusra is the main force there and they are curbing any attempts to negotiate with the government.
"Jabhat al-Nusra has destroyed hospitals and water supplies. Civilians are human shields for terrorists in these cases. The aim of al-Nusra is to attack the humanitarian corridors and the people providing aid."
Churkin told the council that the US had been arming rebel troops in eastern Aleppo.
"In eastern Aleppo, there are about 2,000 people belonging to different branches of the rebels and they have firearms, heavy weapons, armoured vehicles, tanks. They could not have made all these weapons themselves.
"They got their weapons from their very generous Western backers, no doubt headed up by the US coalition."
Using US weapons transfers to Libya as an example, Churkin said that he estimated at least 20,000 tonnes of weaponry had been sent to US aligned forces in Syria.
"Now, I'm just remembering an episode in Libya, an incident that was raised at the US congress and there were questions asked by the Secretary of State, about some countries putting 20,000 tonnes of weapons into Libya," he said. "I'm sure the level of military support in Syria is even higher."