Human Rights Watch says it has evidence that Syrian government forces have carried out hundreds of indiscriminate attacks over the past year with air-delivered munitions, including improvised weapons such as barrel bombs

The US-based group says the attacks have had a devastating impact on civilians, killing or injuring thousands of people.

Barrel bombs are crudely made containers filled with nails, metal shrapnel and explosive which are dropped from helicopters.

Government forces have repeatedly been accused on using these munitions during the war despite a UN resolution last year banning their indiscriminate use in populated areas.

"For a year, the Security Council has done nothing to stop Bashar al-Assad's murderous air bombing campaign on rebel-held areas, which has terrorised, killed, and displaced civilians," said Nadim Houry, deputy Middle East and North Africa director at Human Rights Watch.