Media captionAmateur footage purports to show rebel factions advancing towards AleppoRebel factions in Syria say they have broken a weeks-long government siege of Aleppo, amid scenes of rejoicing in the the crucial northern city.

Sources close to government forces denied that they had been pushed aside and said they had driven the rebels back from an artillery base.

UK-based opposition activists say the rebels have indeed managed to link up with their comrades in eastern Aleppo.

But the rebels have so far failed to establish a secure route, they add.

The rebel coalition includes an al-Qaeda affiliated group.

Government forces cut Aleppo's rebel-held areas off in July, with some 250,000 people living under siege.

Image copyright AFP Image caption Syrians gathered in the street in Aleppo in celebration after rebels said they had broken the government-led siege Image copyright AFP Image caption Opposition officials said they had opened a new route into Aleppo Image copyright Reuters Image caption The city had been under a government-led siege for weeks Image copyright Reuters Image caption Some 250,000 Syrians lived under siege in Aleppo's rebel-held areas Image copyright Getty Images Image caption "White Helmet" rescue workers were among those celebrating Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, a UK-based opposition news service, said the rebels had broken the siege but the route was "not fully secure yet".

On Friday, the rebel groups said they had stormed an artillery base in the city.

But the Syrian army said it had repelled the assault and inflicted heavy casualties on the rebels.

Meanwhile, a US-backed alliance of Kurdish and Arab fighters seized most of Manbij - a key Syrian city - from so-called Islamic State.

Fawaz Gerges, who is professor of Middle Eastern Politics at the London School of Economics, told the BBC News Channel that the rebels had certainly made gains.

"The rebels coalition - it's called the Army of Conquest - has basically made some major progress," he said.

Media captionRebels from the Free Syrian Army released footage of a huge explosion in the Ramouseh district"It has been able to score some major gains in the past 48 hours. The question is not whether the opposition has made some progress or not [but] whether they can really maintain the areas that they occupy and whether they can consolidate it."

The Syrian army has been fighting the rebels with the help of Russian air strikes.

Media captionOne of the few doctors remaining in Aleppo reveals how medics and civilians face death in the city on daily basis.Earlier this week, Russian state television ran pictures of civilians and fighters reportedly leaving the city through humanitarian corridors announced by Moscow.

But some rebel groups described the Russian initiative as a ploy to recapture all of Aleppo.

Aleppo was once Syria's commercial capital and also boasted a rich architectural and archaeological heritage.

Much of it has been destroyed or looted during more than five years of war.