A bomb planted in the car of a Yemeni intelligence colonel exploded on Sunday in the capital, killing the officer and wounding three people, a security official said.
In the south, two soldiers were killed in an attack on their checkpoint.
The attacks were the latest to target military personnel as Yemen grapples with several armed revolts and negotiates a difficult political transition.
The explosive device was planted under the driver's seat in Colonel Mohammed Fadhel Hussein's vehicle, the official said, adding that it exploded as the car passed near the oil ministry in Sanaa.
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A bodyguard travelling with Hussein was wounded, as were two passers-by, the official said.
In the south, gunmen killed two soldiers and wounded a third at a military checkpoint in the port city of Aden, a security official told AFP.
"Two armed men arrived in a car, got out and started firing at soldiers manning a checkpoint at the western exit of Aden, killing two soldiers and wounding one other," the source said.
One attacker was killed in an ensuing gunfight, but the second was able to escape in the car which was driven by an accomplice, the source added.
Similar attacks have been blamed on Al-Qaeda in the Arabian Peninsula, a powerful local affiliate of the global extremist network.