The UN's humanitarian chief Valerie Amos is due to arrive in Syria later to discuss increasing emergency aid to civilians.
During a three-day trip she will also visit Lebanon and hold talks on providing support to refugees.
It comes as foreign ministers to the Organisation of Islamic Cooperation agreed on Monday to suspend Syria. Fifty-five member states approved the recommendation, with only Iran and Algeria against it.
Meanwhile, Syrian rebels are claiming they have shot down a jet and captured its pilot , an apparent victory against the overwhelmingly superior firepower of President Bashar al Assad's forces.
Video uploaded to the internet on Monday showed the jet bursting into flames as it streaked through the sky amid heavy gunfire. The rebels said they had hit it with newly acquired high-calibre anti-aircraft guns.
The government said the plane had crashed due to technical problems while on a "regular training mission".
Rebels also released a video of a man they said was the pilot, identifying him as pilot Mohammed Suleiman, surrounded by three armed men. They said he had been captured after ejecting while his stricken aircraft plunged from the sky.
"We will treat this prisoner according to what is required of us by our religion, our morals and the protocols in the Geneva convention related to prisoners of war," a rebel identified as Captain Abu Laith said in the video.
However, other disturbing footage on YouTube appeared to show rebels meting out violent justice. In one video, dead bodies are thrown from the rooftop of a post office, while a crowd of shouting men watch.
Enraged members of the crowd kick the bodies down stairs and can be heard calling them members of the shabbiha pro-government militia.
Another video a young man being killed by captors who accuse him of being a member of the shabbiha.
Rebels said the video may have been made by government forces to discredit them.
Such images will cause alarm among Western countries that have backed the rebels publicly but are worried about the presence in their midst of hardcore al Qaeda-style Sunni Muslim fighters who use the ruthless tactics that became common in the sectarian bloodbath in neighbouring Iraq.
The shabbiha, mainly drawn from President Assad's minority Alawite sect, have been accused of carrying out massacres of Sunnis.
The downing of a fighter jet would be a rare coup for the lightly armed rebels up against the superior weaponry of Assad's forces, which have made increasing use of air power in recent months.
The Pentagon has said it deplores what it sees as Mr Assad's increasing use of air power but stopped short of suggesting any move towards steps such as a no-fly zone.