Indiscriminate Russian airstrikes on civilian areas have killed hundreds of innocent people and may amount to war crimes, Amnesty International said in a report on Wednesday.

"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. Such attacks may amount to war crimes," said Philip Luther, Director of the Middle East and North Africa Program at Amnesty International.

Since intervening in Syria to bolster the regime of President Bashar al-Assad, Russia has claimed that it is targeting "Islamic State" (IS) and other terrorist groups. The Russian defense ministry has repeatedly denied claims its airstrikes have targeted or killed civilians.

Amnesty examined six airstrikes believed to be carried out by Russia in Homs, Idlib and Aleppo provinces between September and November which it said killed at least 200 civilians and around a dozen fighters.

The airstrikes included attacks on homes, a market, a mosque and field hospital, which Amnesty said the Russian government may have tried to deliberately cover up.

"After some attacks, they (Russian authorities) have responded to reports of civilian deaths by denying they killed civilians; after others, they have simply stayed silent," Amnesty said adding, that in the case of one mosque attack, Russian authorities used deception to cover it up.

Evidence also suggested Russia has used internationally banned cluster munitions and unguided bombs on densely populated civilian areas, Amnesty said. Those findings echo a report released this week by Human Rights Watch that found at least 20 cases of cluster bomb use since Russia and Syria joined a renewed assault on rebels and IS in late September.

The HRW report found the cluster munitions were either made in Russia or the former Soviet Union, but neither Amnesty nor HRW were able to determine with certainty whether cluster munitions attacks were carried out by Syrian forces, Russian forces, or both.

Cluster munitions are indiscriminate and due to the high dud rate pose a long-term threat to civilian populations. Each cluster munitions bomb scatters dozens of bomblets over an area the size of a football field that when dropped in civilian areas violate international law.

An estimated 250,000 people have been killed in nearly five years of conflict in Syria.