A coalition of Syrian Islamist rebel groups has said it stormed an artillery base in the strategic city of Aleppo to try to end a government siege.
The Syrian Observatory for Human Rights, a UK-based monitoring group, said part of the base had been taken.
But the Syrian army said it had repelled the assault, inflicting heavy casualties on the rebels.
Some 250,000 civilians live under siege in Aleppo’s rebel-held areas since government forces cut them off in July.
Also on Friday, the UN said it had for the first time in weeks delivered aid to thousands of Syrian refugees stranded on the border with Jordan.
A group of relief agencies said they had completed delivery of a month’s worth of food and hygiene supplies.
More than 75,000 people had been without aid since June when Jordan sealed the border after a deadly attack there by so-called Islamic State.
The rebel coalition, which includes an al-Qaeda affiliated group, said it had managed to take part of the Aleppo base, which lies about 1.6km (one mile) from the besieged rebel areas of the northern city.
Video footage released by the rebels purports to show fighters inside the facility, inspecting captured weapons and equipment.
Syria’s state-run media said the attack had been foiled and many insurgents had been killed.
Rebel groups are trying to reconnect an encircled area in the east with insurgent territory in the west.
The Syrian army has been fighting the rebels with the help of Russian air strikes.
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.