BEIRUT - Syrian rebels said on Wednesday they had shot down a fighter jet in northern Syria as part of their campaign to weaken the army's overwhelming air power.

Syrian President Bashar Assad, who is struggling to put down a 17-month-old uprising against his rule, has been relying increasingly on aircraft to attack the rebels, who are comparatively lightly armed with machineguns and rockets.

The rebels stepped up their attacks on air bases last week.

Opposition fighters in northern Idlib province said they shot down the aircraft on Tuesday with heavy machinegun fire as it was taking off from the Abu Thuhur air base.

"They brought it down as it was taking off from the airport using 14.5 millimeter anti-aircraft machineguns," said Abu Majad, a spokesman from the rebel Ahrar al-Sham (Free Men of Syria) brigade.

"The airport has been surrounded by the Ahrar al-Sham brigade and the Syrian Martyrs Brigade," but it was not clear if fighting was in progress, he said. "Due to communication difficulties I am not sure what the situation is at the moment."

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