Russia warned Western powers on Monday against any military intervention in Syria, saying the use of force without a U.N. mandate would violate international law.

Foreign Minister Sergei Lavrov said Moscow had no plans to be drawn into a military conflict over the civil war in Syria and that Washington and its allies would be repeating "past mistakes" if they intervened in Syria.

"The use of force without the approval of the United Nations Security Council is a very grave violation of international law," Lavrov told a news conference at which he discussed accusations by rebel forces that Syrian government forces have used chemical weapons.

Russia is Syrian President Bashar al-Assad's key ally and one of its main arms suppliers. It is also a veto-wielding member of the U.N. Security Council, where it has protected Damascus from three consecutive resolutions that were intended to put pressure on him to end violence.

For more than two years, Moscow has demanded that any change of government in Syria must be carried out via a political process in which Assad must be part, and that no talks on Damascus' future can be predicated on Assad's exit from power.

Lavrov said last Wednesday's alleged chemical attack, which U.N. chemical weapons experts began investigating on Monday, was probably the work of rebels who wanted to derail plans by Washington and Moscow to hold talks on Syria's future.

Russian and U.S. officials are expected to meet on Wednesday to look at preparations for the conference.

Expressing concern about statements suggesting NATO had the right to intervene after the chemical attack without securing the approval of the United Nations, Lavrov said the unapproved use of force would "sharply aggravate" the situation.

He urged the West not to go down the "dangerous path" it had taken several times before and added: "We have no plans to go to war with anyone."

"If anybody thinks that bombing and destroying the Syrian military infrastructure, and leaving the battlefield for the opponents of the regime to win, would end everything - that is an illusion," Lavrov said.

French Foreign Minister Laurent Fabius has said Russia and China would probably veto a Security Council vote to allow strikes against Syria. British Foreign Secretary William Hague, however, said it would still be possible to respond to a chemical weapon attack without the Security Council's backing.