Police said the bombs targeting the buses in two different parts of the city exploded simultaneously using remote controlled devices.

A junior naval officer and a civilian female doctor were among those killed in the twin blasts, Pakistan Navy spokesman Commander Salman Ali said.

The Taliban claimed responsibility for the attacks, and vowed more attacks on security forces.

The attack on the military in Karachi was the first since 2004, when gunmen ambushed a convoy escorting the Karachi army corps commander. The general narrowly escaped that attack.

Karachi is Pakistan's biggest city and commercial hub. It hosts the country's central bank, the main stock exchange as well as the two main ports. Most foreign companies working in Pakistan have offices in Karachi, which is also the main base for the navy.