Syrian PM Hijab defects to join revolution
Mr Hijab was appointed less than two months ago and his departure is the highest-profile defection since the uprising began in March 2011.
His family is reported to have fled Syria with him.
A Sunni Muslim, Riad Hijab comes from the Deir al-Zour area of eastern Syria which has been caught up in the revolt.
Mr Hijab is the first cabinet minister to defect.
A month ago, Brig Gen Manaf Tlas, who was considered close to President Assad, also defected. Thirty other generals have crossed the border into Turkey.
Hours earlier, state TV said a bomb had gone off on the third floor of the Syrian state TV and radio building in Damascus, wounding three people.