Damascus, March 18 (IANS): A Syrian military source on Tuesday denied as "baseless" the opposition claims that the Syrian army used a poisonous gas against a rebel-held city in the northwestern province of Idlib.

"These claims are totally far from the truth," the military source told Xinhua on condition of anonymity.

He added that the rebels make up such accusations "every time they receive a big blow from the Syrian army to justify their failure in front of their followers."

Earlier in the day, the UK-based Syrian Observatory for Human Rights, said at least six people were killed by a government troops' gas attack in the city of Sarmin in the countryside of Idlib.

Other activists also posted online photos and video footages, purporting to show people struggling with suffocation.

The deputy head of the exiled oppositional Syrian National Coalition Hisham Marwah said Tuesday that the Syrian forces targeted Sarmin overnight with four barrel bombs, two of which contained Chlorine gas.

The state news agency SANA didn't comment on the incident, but said the Syrian army killed tens of terrorists from the Al Qaeda-linked Nusra Front, including Saudis and Jordanians, in several towns and areas in the countryside of Idlib.

The Syrian opposition previously accused the Syrian government forces of using Chlorine gas in the Eastern Ghouta countryside of the capital Damascus in 2013, an accusation totally denied by the government.