Russia said on Monday it would be "political suicide" for the government of Syrian President Bashar al-Assad if it used chemical weapons against the armed opposition.

Foreign Minister Sergei Lavrov said in an interview released by the English-language state television channel RT that Assad had given Moscow repeated assurances he had no plans to order such an attack.

"I do not believe Syria would use chemical weapons," Lavrov said in comments translated by the channel into English. "It would be a political suicide for the government if it does."

Russia has remained Syria's main ally throughout 21 months of violence that an opposition monitoring group says has claimed more than 44,000 lives.

It scuttled three rounds of UN Security Council sanctions against Assad and condemned Washington for recognising the Syrian opposition as the legitimate voice of the country's citizens.

Moscow's position has frustrated Western attempts to end the bloodshed by forcing Assad from power. Washington has also slammed Moscow's continued military ties with Damascus.

But Russia also remains one of the only nations to remain in constant contact with Assad -- a status the West has urged it to use to pressure the Syrian strongman to cede power.

Lavrov said Moscow checks on every report about the movement of Syrian chemical weapons with Damascus in order to make sure there was no danger of their possible use.

"Every time we hear rumours, or pieces of information come to surface that the Syrians are doing something with the chemical weapons we double-check, we triple-check, we go directly to the government and all the time we get very firm assurances that this is not going to be used under any circumstances," Lavrov said.