Syria has dismissed US and British claims that it may have used chemical arms as a "barefaced lie" and its ally Russia has warned against using such fears to use military action.

"Statements by the US secretary of state and British government are inconsistent with reality and a barefaced lie," said Omran al-Zohbi, Syria's information minister, in an interview published on Saturday on the Kremlin-funded Russia Today's website.

"I want to stress one more time that Syria would never use it - not only because of its adherence to the international law and rules of leading war, but because of humanitarian and moral issues," Zohbi said.

Zohbi spoke out as UN chief Ban Ki-moon called on Damascus to approve a UN mission of inspectors to probe the alleged use of chemical weapons in the conflict that erupted in March 2011.

But Zohbi told Russia Today television station that Syria could not trust UN inspectors from Britain and the United States.

'Game-changer'

"We also do not trust their qualifications. Their aim is to juggle with facts." he said.

"We won't mind if Russians would be among the experts; quite the contrary, we only welcome this idea. We are quite sure in their high qualification and ability to clearly see into such matters."

Russia and China have blocked several UN Security Council draft resolutions that threatened sanctions against President Bashar al-Assad's regime.

US President Barack Obama said on Friday that using chemical weapons would be a "game-changer", after the US, Israel and Britain cited signs that Assad's regime had used the deadly agent sarin.

But Obama said Washington must act prudently and establish exactly if, how and when such arms might have been used. He promised a "vigorous" US and international investigation into the latest reports.

British Prime Minister David Cameron said the growing evidence that Assad had turned chemical agents on his own people was extremely serious.

Mikhail Bogdanov, Russia's deputy foreign minister and Middle East envoy, urged against using these reports for military intervention.

Military success

"We must check the information immediately and in conformity with international criteria, and not use it to achieve other objectives," he said in Beirut.

"It must not be a pretext for an intervention in Syria."

Zohbi said in comments published by the Interfax news agency on Friday that chemical weapons were used by opposition fighters and originated in Turkey.

He linked the chemical arms accusations to what he said was the recent military success of regime forces.

"There are qualitative changes on the battlefields," Zohbi was quoted as saying by the RIA Novosti news agency.

"The uproar from the Americans that has arisen in the last 48 hours is due to this."

Reuters news agency reported that amateur video appeared to show aerial bombardments on opposition strongholds around Syria's capital Damascus.

Assad gains

Assad's forces appeared to have made gains across Syria in recent weeks, Reuters reported.

They have advanced around Damascus and the border with Lebanon, areas that help link the capital to coastal provinces dominated by Assad's Alawite minority.

The government was pounding opposition strongholds with air power and shelling in an effort to gain the upper hand in a war that had already killed 70,000 people, Reuters said.

The Syrian opposition urged the UN Security Council to take immediate steps, possibly even by imposing a no-fly zone on Syria.

Yasser Tabbara, spokesman for the Syrian interim government of Prime Minister Ghassan Hitto, said: "What we are asking the international community, what we are asking the United States, with its drone technology, with its surgical strike technology, is to help us disable Bashar al-Assad from the use of these chemical weapons."

Fighting continued unabated on Saturday, with at least 10 people killed in shelling on Douma north-east of Damascus, the Syrian Observatory for Human Rights said.