It hit as the bus was passing through the Dar Silm district, taking officers and troops to work.
The officials say they are investigating whether the explosion was caused by a bomb hidden on the bus, a roadside device or a suicide bomber. They spoke on condition of anonymity according to regulations.

Yemen, the Arab world's poorest country, is plagued by an al-Qaida insurgency and has seen scores of attacks on its military or security forces.
In August, a bomb hidden on a bus carrying air force personnel in Sanaa killed three people and wounded 23.


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