A donkey cart carrying a suspected improvised bomb blew up at a checkpoint on the Kenya-Somalia border Thursday, killing one Kenyan police officer and critically wounding four others, authorities said.

A Kenyan police report seen by The Associated Press said the cart pulled by two donkeys and ridden by one man passed the Somali checkpoint of Bula Hawa and entered Kenyan territory, where it was stopped by officers to check the load.

The rider jumped off and ran back into Somalia moments before the cart exploded, causing a huge fire at the border post in the northern county of Mandera, the report said.

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No one claimed responsibility for the attack, but suspicion immediately fell on al-Shabab, a Somalia-based extremist group linked to al-Qaida.