Moscow is supplying arms to Syria under Soviet-era commitments and were meant for defence against external threats, not to support President Bashar al-Assad, Russia's foreign minister told an Egyptian newspaper.

Russia sold the Syrian government $1 billion worth of weapons last year and has made clear it would oppose an arms embargo in the United Nations Security Council, contending that rebels would get weapons illegally anyway.

Russian Foreign Minister Sergei Lavrov told Egypt's state al-Ahram daily in an interview published on Monday that the arms still being sent to Damascus were part of old Soviet contracts and did not violate international law.

"We do not side with any faction in Syria's internal battle," Lavrov was quoted as saying. "As for the Russian-Syrian technical military cooperation, it aims to support Syria's defence capabilities in the face of external political threat, and not to back Bashar al-Assad."

He accused foreign powers of arming the opposition to topple the government in breach of international law, adding that such weapons could fall into the hands of al Qaeda fighters.

Western powers back the rebels but say they have stopped short of sending arms. Qatar, which has been an outspoken critic of Assad and called for a no-fly zone, has also denied providing arms but says it does give logistical and humanitarian support.

"It was the Soviet Union that supplied Syria with main weapons but at present we are in the process of finalising the implementation of our commitments which are linked primarily to the supply of some air defence systems," Lavrov told al-Ahram.

"These military exports are of a defensive nature and do not conflict with international treaties," he said.

A Russian official said in July the Moscow would not deliver fighter planes or other new weapons to Syria while the conflict there remained unresolved.

Russia and China, both permanent Security Council members, have vetoed three Western-backed U.N. draft resolutions condemning Assad's government for its handling of the uprising that began with peaceful demonstrations in March 2011.

The protests turned into an armed revolt after Assad used force to crush opposition. About 32,000 people have been killed.

Lavrov, who met Lakhdar Brahimi, the international mediator on Syria, in Cairo on Sunday, said the Syrian government and the opposition should be forced to sit down to negotiations. Lavrov was due to meet the Egyptian foreign minister later on Monday.