The number of people killed in last week's devastating bombing in the Somali capital Mogadishu has risen to 358, according to the government.

As well as the confirmed death toll, 228 people were injured in what was the deadliest attack in the country's history, Somalia's news agency quoted the information and internal security ministers as saying late on Friday.

The announcement came as a car bomb exploded outside Mogadishu, killing the driver, police said, with a witness saying there were at least two bodies.

The explosion happened around noon in the village of Markaz, about 20km northwest of Mogadishu, Police Major Nur Ali told Reuters news agency.

He said police had not reached the scene, which he called an area "inhabited by hardline Islamists".

A witness in the village who gave his name as Ahmed told Reuters by telephone that he had seen two dead bodies.

"The car was ruined and the dead bodies were cut in halves," he said.

The armed group al-Shabab was blamed for Saturday's blasts, which happened when a car bomb and a truck bomb headed for the airport detonated prematurely.