The rebel Free Syrian Army categorically rejected Thursday a Russian proposal for placing Syria's chemical arms under international control, and called for regime officials to be brought to justice.

The Syrian National Coalition opposition group also questioned the initiative, calling it a "political manoeuvre aimed at buying time" for the regime of President Bashar al-Assad.

"The Free Syrian Army announces its categorical rejection of the Russian initiative that foresees placing chemical weapons under international control," FSA military commander General Selim Idriss said in a video posted on YouTube.

Idriss told world powers they should not "be satisfied only by removing the chemical weapon, which is the tool of a crime, but judge the author of the crime before the International Criminal Court, who has clearly acknowledged possessing it and agreed to get rid of it."

Assad told Russian television Thursday that Syria would place its chemical weapons under international control but emphasised the move was prompted by Moscow, not US threats of military action.

Questioning the motives for the initiative by Russia, a close ally of Assad, the Coalition's overnight statement also said it would be unacceptable unless it "called to account the crimes against the Syrian people".

And any measures should be adopted under Chapter VII of the UN Charter, which allows for possible military measures.

It said that if the "response to Syria of the international community is not efficient and effective, Iran, North Korea and the militia of Hezbollah (Lebanon's powerful Shiite movement and an Assad ally) will consider it a green light to manufacture and use chemical weapons".

Idriss also called on countries backing the 30-month uprising against Assad to increase the supply of arms to the rebels so that they can "continue to liberate the country".

And he exhorted his fighters to "intensify operations in all regions of the country".

Syria's Muslim Brotherhood issued its own rejection of the Russian initiative and "any attempt to reach a settlement with the criminal regime."

It criticised any attempt to strike a deal "with those who committed genocide in cold blood with chemical weapons".

The group, which belongs to the Syrian National Coalition, called on the international community to "end political uncertainty and act... to prevent Assad from committing additional massacres".

The United States claims that the regime carried out chemical weapons strikes on a number of Damascus suburbs on August 21, killing more than 1,400 people, and threatened to launch punitive strikes.

The regime has denied responsiblity for the attack.

Russia on Monday announced a proposal under which Syria would turn over its chemical weapons, and US President Barack Obama postponed any military action to consider the Russian initiative.

The four-point plan, details of which were disclosed on Wednesday, would see Syria becoming a member of the Organisation for the Prohibition of Chemical Weapons, according to a report in Moscow.

Syria would then have to declare the location of chemical weapons arsenals and, then allow OPCW inspectors to examine them and finally decide, in cooperation with the inspectors, how to destroy them.

UN inspectors have already visited the sites of the alleged attacks in Damascus, and France has said their report will probably be issued on Monday.

Foreign Minister Laurent Fabius told French radio Thursday "it will say that there was a chemical massacre" and that "there will certainly be indications" of the origin of the attack.