AMMAN - Syrian rebels besieging a military airport near the border with Iraq were involved in serious fighting on Wednesday, opposition sources said, as rebels in the north of the country said they had shot down a fighter jet.

Free Syrian Army rebels have been laying siege to Hamadan airport in the city of Albu Kamal on the country's eastern frontier in Deir al-Zor province for the past three days.

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

The opposition said the airport, where dozens of soldiers are still holding out, has been used by helicopters to launch bombing runs against rebel strongholds.

The rebels stepped up their attacks on air bases last week in an attempt to blunt Assad's air power which he has deployed to try to check rebel advances in urban and rural areas in the last month.

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