Syrian fighter jets bombed the Palestinian Yarmouk camp in Damascus on Sunday, killing at least 25 people sheltering in a mosque in an area where Syrian rebels have been trying to advance into the capital, opposition activists said.

The attack was part of a month-old campaign by President Bashar al-Assad's forces to eject rebels fighting to overthrow him from positions hemming in Damascus. Yarmouk, on the southern fringes of the Syrian capital, falls within a swathe of territory running from the east to southwest of the city from where rebels hope to storm into the main redoubt of Mr. al-Assad.

In Paris, French Foreign Minister Laurent Fabius said he believed the Syrian ruler would fall soon. "I think the end is nearing for Bashar al-Assad," Mr. Fabius told RFI radio.

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He described the attack on Yarmouk as scandalous. "You have to ask yourself whether President Assad is not trying to enflame the region (through it)," the minister said.

Taking an opposing line to that adopted by France, Hezbollah leader Sayyed Hassan Nasrallah said the rebels could not win in Syria.

"The situation in Syria is getting more complicated [but] anyone who thinks the armed opposition can settle the situation on the ground is very very very mistaken."

Syrian rebels accuse Hezbollah, a Shi'ite Muslim group based in Lebanon, of sending fighters to neighbouring Syria to help Mr. al-Assad overcome the largely Sunni Muslim revolt. Hezbollah denies these accusations.

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In the latest of a string of military installations to fall to the rebels, the army's infantry college in northern Aleppo was captured on Saturday after five days of fighting, a rebel commander with the powerful Islamist Tawheed Brigade said.

Opposition activists said the deaths in Yarmouk, to which refugees have fled from other fighting in nearby suburbs, resulted from a rocket fired by a warplane hitting the mosque.

A video posted on YouTube showed bodies and body parts scattered on the stairs of what appeared to be the mosque.

The latest battlefield accounts could not be independently verified due to tight restrictions on media access to Syria.

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It was the first reported aerial attack on Yarmouk since a popular uprising against Mr. al-Assad erupted 21 months ago and evolved, after he tried to smash it with military force, from peaceful street protests into an armed insurgency.

Syria is home to more that 500,000 Palestinian refugees, most living in Yarmouk, and both Mr. al-Assad's government and the rebels have enlisted and armed Palestinians as the uprising has mushroomed into a civil war.

Heavy fighting broke out 12 days ago between Palestinians loyal to Mr. al-Assad and Syrian rebels, together with a brigade of Palestinian fighters known as Liwaa al-Asifah (Storm Brigade).

Clashes flared anew after Sunday's air strike between Palestinians from the pro-Assad Popular Front for the Liberation of Palestine-General Command (PFLP-GC) and Syrian rebels together with other Palestinian fighters, according to the Syrian Observatory for Human Rights monitoring group.

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Some PFLP-GC fighters were killed, the London-based Observatory said.

Opposition activists and the Observatory said many families were trying to escape the internal Yarmouk clashes.

In Aleppo, Syria's biggest city, insurgents first reported seizing the infantry college on Saturday, but the Syrian Observatory for Human Rights said later that day there was still fierce fighting going on.

The commander whose Tawheed brigade took part in the assault said the rebels had surrounded the college, located 16 kilometres north of Aleppo, Syria's largest city, three weeks ago.

"At least 100 soldiers have been taken prisoner and 150 decided to join us. The soldiers were all hungry because of the siege," the commander, who spoke on condition he was not further identified, told Reuters by telephone.

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More than 40,000 Syrians have now been killed in what has become the most protracted and devastating of the Arab popular uprisings that have toppled several dictators since early 2011.

Desperate food shortages are growing in parts of Syria and residents of Aleppo say fistfights and dashes across the civil war front lines have become part of the daily struggle to secure a loaf of bread.

Violence continued across the country. Syrian forces killed 25 people in the town of Helfaya in Hama province when they shelled it with warplanes and artillery for the first time since February, opposition activists said.

A Youtube video showed at least three bodies lying in a street and several more inside cars.

An activist who declined to be named said the town, a rebel stronghold, came under fire after insurgent fighters attacked several checkpoints just outside it.

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Ten fighters were killed in shelling in Deraa, the cradle of the revolt against Assad.

Damascus has accused Western powers of backing what it says is a Sunni Islamist "terrorist" campaign to topple Mr. al-Assad, a member of the minority Alawite sect affiliated with Shi'ite Islam. It says that U.S. and European concerns about Mr. al-Assad's forces possibly resorting to chemical weapons could serve as a pretext for preparing military intervention.

But, unlike NATO's air campaign in support of Libya's successful revolt last year against Moammar Gadhafi, Western powers have been wary of intervening in Syria.