The convoy was returning from the airport, where the bodies of four Ugandan peacekeepers were flown home after they were killed on Wednesday.

This is the third apparent attempt to kill Mr Ghedi since he took office. Somalia's government has blamed previous such attacks on al-Qaeda.

"One of two men suspected of planting the bomb was captured on the site," government spokesman Abdullahi Muhyidin Mohamed told Reuters news agency.

At least two Somali police officers have been shot dead since Wednesday as they took part in a clear-up operation in the main Bakara market.

'Terrorist attack'

Uganda says it will not pull out its troops from Somalia, despite Wednesday's attack. "It is a terrorist attack to try and intimidate our force. But those are kicks of a dying horse," Gen Nyakairima said.

It was the deadliest attack on the Ugandan peacekeepers since 1,600 soldiers were deployed to Somalia in March, as part of an African Union mission. A proposed 8,000-strong force is due to take over security duties from the Ethiopian army.

The government last month said it had defeated Islamist insurgents after weeks of bloody fighting, which killed some 1,300 people and led some 300,000 to flee their homes.

'Noble action'

AU commission chairperson Alpha Omar Konare condemned the attack on the peacekeepers and urged the Uganda soldiers to remain engaged in the "noble action" of helping Somalia.

Ethiopia's troops have been in Mogadishu since December at the invitation of Somalia's transitional government fighting Islamist insurgents and clan militiamen.

The attack came a day after Somali President Abdullahi Yusuf held talks with his Ugandan counterpart Yoweri Museveni in Kampala over the mission.

Mr Konare appealed to western governments to support the AU mission to enable it carry out its mandate in Somalia. Ghana, Malawi, Nigeria and Burundi have pledged to deploy troops for the AU mission but they are yet to announce the dates.