A Syrian air force pilot flew his fighter plane over the border to Jordan and was granted political asylum.
This is the first defection with a military aircraft since the start of the uprising against President Bashar al-Assad.
Colonel Hassan Hamada landed at the King Hussein Military Air Base 80km northeast of Amman, Jordan seeking asylum.
Syria's Defence Ministry has called the pilot a "traitor to his country and his military honour" saying it would punish Hamada under military law and sought to retrieve the aircraft.
The defection will boost the morale of the rebels as Assad's forces intensify efforts to crush the uprising and international peace efforts are stalled.
Thousands of soldiers have deserted in the 15 months since the revolt broke out.
But unlike last year's uprisings in Libya and Yemen, no members of Assad's inner circle have broken with him.
The army today maintained its bombardment of downtown areas of Homs despite a temporary truce that had been agreed to allow the evacuation of civilians and the wounded.
Aid workers from the International Committee of the Red Cross and Syrian Arab Red Crescent were forced to turn back because of shooting.
In Douma, a conservative Sunni suburb of Damascus 20 people were killed in shelling by the army.
Rebels fought tank-backed forces to prevent them from advancing into the district, home to 300,000 people.
Reports from Syria cannot be independently verified as state authorities have barred international journalists and rights groups.