Radical Islamist rebels on Sunday seized large swathes of a Syrian military base west of Aleppo, as they consolidated their control over territory in the north near the Turkish border, an AFP journalist said.
Sheikh Suleiman base sprawls over nearly 200 hectares (500 acres) of rocky hills about 25 kilometres (15 miles) from Aleppo city, an area now almost completely under rebel control.
Fighters hoisted a trademark black jihadist flag over one of the buildings they captured in the morning as firefights persisted with light weapons as they tried to take the rest of the base.
Many of the fighters are non-Syrian and one of their leaders, who identified himself as Abu Talha, said he is from Uzbekistan.
"Here we are all Muslims," Abu Talha said of the militants.
One fighter added: "We are all mujahedeens and muhajereens (companions of the Prophet Mohammed)."
The militants refused to say which group they belong to, and Abu Talha barred combatants from other factions from entering the combat zone.
The AFP correspondent said fighters from the main rebel Free Syrian Army did not take part in the battle for Sheikh Suleiman, and that only a small FSA group in nearby villages monitored the battle through binoculars.
"The Islamists caught us unawares by launching an attack on their own against the base on Saturday night," said an FSA fighter. "They were quicker than us."
Earlier, the Britain-based Syrian Observatory for Human Rights said the rebels took control of Regiment 111 and three other company posts inside the base after fierce overnight clashes.
"Two rebels and one soldier were killed, while five soldiers were captured. The prisoners said that 140 of their men had fled to the scientific research centre on the base," Observatory director Rami Abdel Rahman told AFP.
The rebels said they seized large quantities of hardware, including three anti-aircraft batteries and mortar ammunition. "There's a lot of arms still on the base," one of them said.
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Government troops were holed up in "scientific research centre," some of them wearing gas masks, he added.
On Saturday an FSA commander, Sheikh Azam Ajamar, had said his troops would not use heavy weapons to attack the base to avoid damaging the research centre. "There is strong probability that chemical arms are there," he claimed.
Three FSA brigades -- Nureddin Zinki, Al-Beit and Al-Ansar, whose ranks comprise mostly Islamist fighters -- have laid siege to the base for several weeks.
The proliferation of Islamists in the 21-month conflict has stoked fears among world powers wary of providing weapons to rebels battling President Bashar al-Assad's regime, lest they fall into extremist hands.
On Sunday the rebel ambassador to France, Monzer Makhous, warned in a newspaper interview that the "passivity" of the international community was boosting the rise of Islamist extremism in his war-torn country.
Makhous also urged the lifting of a European Union arms embargo.
Elsewhere in northern Syria, 10 people were reported killed in regime bombardment of the town of Maraayan, while five civilians including a child were killed as Ahsam village in Idlib province was shelled, the Observatory said.
The watchdog also reported clashes around the Wadi Deif military base, which rebels have been trying to take since seizing the nearby town of Maaret al-Numan two months ago.
Fighting also raged in around the capital Damascus, including the southern Qadam neighbourhood.
Activists posted an Internet video of a large fire in the Port Said area of Qadam. "The Free (Syrian) Army hit the checkpoints," the cameraman says, as machinegun fire is heard.
The military has for several days bombarded rebel strongholds in the suburbs, including from the air, raising fears of a looming ground assault by the army to try to establish a secure cordon around the capital.
The Observatory, which relies on a countrywide network of activists and medics, gave an initial toll of 61 people killed nationwide on Sunday, adding to more than 42,000 dead since the uprising erupted in March last year.
Across the border in Lebanon, meanwhile, sectarian clashes linked to the conflict in Syria killed six people and wounded 40 in the northern city of Tripoli, a Lebanese security official said.