A report by Amnesty International focused on six strikes on the Homs, Idlib and Aleppo provinces which "may amount to war crimes."

Amnesty's Philip Luther, said: "Some Russian air strikes appear to have directly attacked civilians or civilian objects by striking residential areas with no evident military target and even medical facilities, resulting in deaths and injuries to civilians."

The group said at least 200 civilians were killed in the strikes between September and November.

It denounced Russia's "shameful failure" to acknowledge civilian killings.

Last week New York-based Human Rights Watch said cluster munitions were used on at least 20 occasions since Syria and Russia began their joint offensive on 30 September.

Russian officials have repeatedly rejected such accusations, and residents and opposition activists inside Syria acknowledge they have no way of knowing for sure whether the attacks are carried out by Russia or the Syrian military.

Russian President Vladimir Putin's spokesman Dmitry Peskov has insisted its military in Syria operates in line with international law.

"Russia is conducting its operation in strict conformity with principles and norms of the international law, including those sections of the international law that regulate using and bans on using one or another type of weapons."