Moscow accused Washington Thursday of prolonging the Syrian conflict by supporting the opposition, on the eve of a UN Security Council vote that threatens to further deepen divisions between major powers.

On the ground, a car bomb exploded at a border crossing between Syria and Turkey as rebels battled to prevent regime forces from seizing their last stronghold in the strategic Qalamun region.

And Syria's government media said Jordan was seeking to stir up the southern front in the country's conflict after a stalemate in peace talks held in Geneva this month.

Speaking in Baghdad, Russia's Foreign Minister Sergei Lavrov said America's policy on Syria "encourages extremists who are financing terrorism and supplying terrorist organizations and groups with weapons."

"In the end, this will not result in anything except the escalation of the Syrian conflict," he said in remarks translated from Russian into Arabic.

Moscow is a key backer of President Bashar al-Assad's regime, which has been battling an uprising that began in March 2011.

It supplies the government with weapons and provides diplomatic cover at the UN, where the Security Council is expected to vote Friday on a resolution on humanitarian aid for Syria.

The draft resolution was presented on Thursday but does not so far have Russian backing.

It calls on all parties to end sieges of densely populated areas immediately, including in central Homs, the Palestinian Yarmuk camp in Damascus and Ghouta on the outskirts of the capital.

It also calls for an immediate end to all attacks on civilians and for all parties, in particular the Syrian authorities, to authorize humanitarian groups to deliver aid across front lines and borders.

A source in The Hague, meanwhile, said Syria was likely to miss a UN-backed June 30 deadline to destroy its chemical arsenal, possibly by months.

An Organisation for the Prohibition of Chemical Weapons (OPCW) meeting on Friday is expected to hear calls for Syria to do more amid Western frustration with Damascus' perceived delays.

Reuters