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 yesterday, Russia's Foreign Minister Sergei Lavrov said America's policy on Syria "encourages extremists who are financing terrorism and supplying terrorist organisations and groups with weapons".
Moscow is a key backer of President Bashar al-Assad's regime, which has been battling an uprising that began in March 2011.
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It supplies the government with weapons and provides diplomatic cover at the United Nations, where officials said the Security Council is to vote tomorrow on a resolution on humanitarian aid for Syria.
Russia, with support from China, has blocked three previous resolutions aimed at pressuring the Damascus regime since the crisis began, with an estimated 250,000 people across Syria awaiting help.
It also demands the "the immediate cessation of all attacks against civilians", such as through the use of barrel bombs, a clear reference to Syrian army tactics used in Aleppo, in the north.
And it calls for all parties, in particular the Syrian regime, to authorise humanitarian groups to deliver aid across front lines and borders.
Humanitarian groups have been seeking cross-border access for some time to allow aid to be shipped directly into Syria from neighbouring countries such as Iraq or Turkey.
The resolution was submitted by Australia, Luxembourg and Jordan, and is backed by Britain, the US and France.
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.