MOGADISHU (AFP) - A huge car bomb blast shook Somalia's capital Mogadishu on Sunday after a suicide bomber struck an area close to the heavily-fortified international airport, killing four people, officials said.

A Somalia police official said the car bomber rammed an explosives-laden vehicle into another car, setting off a huge blast that was heard across the coastal city.

The sprawling airport area is a major base for members of Somalia's armed forces, houses several foreign embassies and African Union troops battling Al-Qaeda-affiliated Shebab militants.

It has been a frequent target of attacks by the Shebab, most recently in late December when the Shebab launched a major assault against an African Union command centre.

"We had information about this car laden with explosives and we have been following it... but it detonated and four civilians were killed, and the bomber," interior ministry spokesman Mohamed Yusuf told reporters Witnesses said they saw clouds of smoke after the explosion, and that security forces opened fire to disperse approaching onlookers.

Several witnesses also said they saw up to five destroyed vehicles in the vicinity of the explosion.

"There was a terrible explosion. The security forces have cordoned off the area. They opened fire to disperse people nearby," said Ali Suleyman, a witness.

The latest attack came at the end of a week which saw the United States conduct another air strike against the Isl.

The Somali government said the Shebab's intelligence chief, Abdishakur Tahlil, was killed in Monday night's raid.

The Shebab's former leader Ahmed Abdi Godane was also killed by a US air strike in September.

The Shebab emerged from the Islamic Courts Union that controlled Mogadishu in 2006 before being pushed out by Ethiopian forces.

The militants were finally driven from their fixed positions in Mogadishu in 2011, and have lost several strongholds in the south and centre of the country in a recent offensive by the AU's AMISOM force.

The group, however, still controls vast rural areas from where militants launch regular attacks against the AU's AMISOM troops and the country's internationally-backed government.