A bomb hidden in a plastic bag exploded at a checkpoint in the Yemeni capital Sanaa on Saturday, killing three policemen and wounding a fourth, a security services official said.
The device was planted near a police checkpoint in the north of the capital and detonated as the policemen opened the bag to check its contents, the official added.
The blast killed two of the policemen immediately and seriously wounded two others, one of whom died later.
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A manhunt has been launched for those behind the attack, the official added.
Saturday's deadly blast came after a period of relative calm in the Yemeni capital.
Yemen's politicians are currently taking part in a national dialogue aimed at paving the way for a new constitution and planned February 2014 general elections.
The impoverished Arabian Peninsula country has been hit by violence attributed to Al-Qaeda militants, southern separatists and a Shiite rebellion in the north.