An alleged chlorine gas attack by the Syrian regime in an opposition-held town is evidence of new war crimes, right body Amnesty International has said.

The London-based human rights organization said on Tuesday that the alleged chlorine gas attack in Idlib that activists said killed an entire family, is evidence of more war crimes by the Syrian regime.

"These horrific attacks that resulted in civilians, including small children, suffering excruciating deaths, are yet more evidence that the Syrian regime forces are committing war crimes with impunity," said Philip Luther, Middle East and North Africa Programme Director at Amnesty International.

"The situation in Syria must be referred to the International Criminal Court as a matter of urgency."

Three children, their mother and father, and their grandmother suffocated to death after the barrel bomb attack in the town of Sarmin in southeast Idlib province, the Syrian Observatory for Human Rights said.

The Britain-based monitoring group told AFP news agency that doctors in Sarmin concluded that the manner of death indicated a gas, possibly chlorine, had been emitted from the barrel bombs.

A Syrian military spokesperson has denied responsibility for the attacks.

'Ruthless airstrikes'

Amnesty also said in another report on Tuesday that the Syrian regime attack on a bastion of the Islamic State of Iraq and the Levant (ISIL) group in 2014 killed 100 civilians and carries "every indication of being war crimes".

Amnesty defined the attack launched by the regimein November 2014 on the city of Raqqa as a series of "ruthless air strikes".

It said the strikes carried out between November 11 and 29 killed 115 civilians, including 14 children, and hit non-military targets including a mosque, a transport hub and a busy market.

Raqqa is the self-proclaimed capital of ISIL, but Amnesty said there was no indication that fighter positions were the target of the series of strikes.

"Syrian government forces have shown flagrant disregard for the rules of war in these ruthless air strikes," Amnesty's Luther said.

"The government appears indifferent to the carnage caused by these strikes, refusing even to acknowledge civilian casualties they have caused."

Luther acknowledged that Raqqa is a stronghold of ISIL members, but said their presence did not justify attacks on civilian targets.

PHOTO CAPTION

A chlorine-tinged cloud of smoke rises into the air from a bomb detonated by Iraqi army and Shi'ite fighters from Hashid Shaabi forces, in the town of al-Alam in Salahuddin province March 10, 2015.

Aljazeera