ALEPPO, Syria (AFP) -- Fighting intensified in Syria‘s two main cities on Tuesday after rebels claimed they downed a government fighter jet and captured its pilot in what would be a major coup for the opposition.

With Bashar al-Assad’s embattled regime facing mounting diplomatic pressure, a top presidential aide was to hold talks in China, which has called for an immediate ceasefire and political dialogue to end the brutal 17-month conflict.

China and Russia are deeply at odds with the West over how to end the bloodshed, after both traditional Syria allies vetoed three U.N. Security Council resolutions, leaving the international community deadlocked on the crisis.

Bouthaina Shaaban, a “special advisor” to Assad, is to hold talks with Foreign Minister Yang Jiechi and other officials, the foreign ministry said, adding that Beijing was also considering inviting members of the Syrian opposition to visit soon.

UN humanitarian chief Valerie Amos is meanwhile due in Syria on Tuesday “to draw attention to the deteriorating humanitarian situation” and discuss ways of scaling-up relief efforts, her office said.

Over one million people have been displaced by the fighting and another 140,000 have fled to Syria‘s neighbors, the U.N. says, many of them living in tent camps in sometimes miserable conditions.

Many areas engulfed in the relentless fighting in Syria are also facing a desperate plight, suffering from food shortages, power outages and lack of medical supplies.

Assad’s regime is also facing pressure from fellow Muslim states as the Organization of Islamic Cooperation meets Tuesday to discuss a recommendation for Syria to be suspended from the 57-nation body.

On Monday, the rebel Syrian Free Army claimed it had shot down a government warplane in the eastern province of Deir Ezzor and issued a video of a man it said was the captured pilot.

FSA spokesman Kassem Saadeddine identified the pilot as Colonel Mufid Mohammed Sleiman and said he was a member of Assad‘s Alawite minority community and a “staunch enemy of the revolution.”

If confirmed, the attack would be the first time the rebels -- who have been demanding anti-aircraft weapons in the face of escalating attacks from the sky -- succeeded in downing a Syrian military plane since the conflict erupted.

State media said that a military plane on a training mission crashed in the east after suffering a malfunction and that the pilot had ejected.

Washington said Assad’s government was employing more air power in its war with the rebels, which activists say has now killed over 21,000 people since March last year.

“We‘ve seen a very troubling and despicable uptick in attacks from the air, perpetrated by the Syrian regime,” Pentagon spokesman George Little told reporters.

Asked if the Pentagon was moving towards enforcing a possible no-fly zone, he said: “We plan for contingencies.”

White House spokesman Jay Carney said the administration has “ruled out no option” in trying to bring about a political transition, but did not explicitly refer to a no-fly zone.

Opposition umbrella group the Syrian National Council also issued a new appeal for the establishment of no-fly zones similar to those set up over Libya during last year’s conflict.

The opposition has accused the regime of increasingly resorting to firing from fighter planes, particularly on the second city of Aleppo, often the scene fierce urban combat and thundering air strikes since late July.

The northern metropolis is seen as pivotal to the outcome of the conflict, with some referring to it as Syria‘s Benghazi, the Libyan city that was the cradle of the revolt against Moamer Kadhafi’s regime.

On the ground Tuesday, fresh fighting erupted in Aleppo, where the army shelled several rebel-held areas, the Syrian Observatory for Human Rights said, after a bloody day in which 160 people were killed nationwide.