A leading international rights group says Russian and Syrian forces have renewed their use of cluster bombs against civilians and rebels in northern Syria.

In a new report released on Thursday, Human Rights Watch documented 47 instances in which cluster munitions were used in attacks by pro-government forces across northern Syria in the past two months.

The New York-based watchdog says the attacks have killed and wounded dozens of civilians.

Cluster munitions, which explode in the air, release hundreds of tiny bomblets, posing a long-lasting danger to civilians. Over 100 countries have signed on to a treaty prohibiting their use.

Syria's air force also used barrel bombs — large, metal containers filled with explosives and metal shards that are pushed manually from aircraft and detonate on impact with the ground.