The Syrian government and so-called Islamic State (IS) militants used chemical weapons during attacks in Syria in 2014 and 2015, a UN report has found.

The report, carried out in conjunction with the Organisation for the Prohibition of Chemical Weapons (OPCW), accused the Assad regime of using chlorine gas in two attacks and IS fighters of using mustard gas in one assault.

The UN-OPCW investigative team was formed by the UN Security Council a year ago to identify parties responsible for chemical attacks in Syria.

It examined nine cases in seven towns where chemical weapons were believed to have been used, and identified responsible parties in three cases.

The team said evidence in three other cases suggested government responsibility, but was not conclusive. Findings in three further cases were inconclusive.

Between December 2015 and August 2016, the UN-OPCW investigators said they received more than 130 new allegations from UN member states of use of chemical weapons or toxic chemicals as weapons in Syria.

US ambassador to the UN Samantha Power said the Syrian government had breached a September 2013 agreement under which the Assad regime agreed to relinquish its chemical weapons stockpile.

Power called on the Security Council to take "strong and swift action" against those accused of using chemical weapons.

France's ambassador to the UN, Alexis Lamek, also called for the Security Council to take action.

"When it comes to proliferation, use of chemical weapons, such weapons of mass destruction, we cannot afford being weak and the council will have to act," he said.

The US National Security Council spokesman Ned Price added: "We continue to remove leaders from the battlefield with knowledge of these weapons and will target any related materials and attempts to manufacture such chemicals going forward."

The Security Council is scheduled to discuss the report on August 30, but it is not clear if any action will be agreed.

Although Moscow supported the establishment of the UN-OPCW investigation, it has blocked sanctions and other action against the Assad regime, which is a close ally.