Somali Prime Minister Ali Mohamed Gedi has spoken of his anger after surviving at assassination attempt in the capital, Mogadishu, at the weekend.
Prime Minister Gedi was on a visit to Mogadishu
"It was a barbaric action, implemented by cowards," he told the BBC.
A convoy in which he was travelling was attacked and at least five people were killed, though Mr Gedi escaped unhurt.
UN special envoy Francois Fall said it was "an assault on the peace process, and on the hopes of the Somali people for an end to 14 years of insecurity".
Mr Gedi was visiting from Jowhar, where one faction of the transitional government, led by President Abdullahi Yusuf, is based.
Some ministers, including the speaker of parliament and former warlords, have based themselves in Mogadishu and refused to move to Jowhar.
Somalia has been without a functioning national authority for 14 years and a transitional government, sworn in last year, has failed to end the anarchy.
'Gunmen and grenades'
Mr Gedi was making his second visit to Mogadishu since his appointment at the helm of the transitional government.
Officials said he was travelling from the airport into the centre of the city when his convoy was attacked by gunmen, who hurled grenades and detonated a landmine.
The blast is reported to have hit one of the vehicles in the convoy, and the prime minister's vehicle was also damaged.
At least one of Mr Gedi's bodyguards was reported to be among the dead.
The defiant PM described the attack as "terrorist action" aimed at blocking the activity of the transitional federal government and sabotaging the peace process.
He said an inquiry would establish who was responsible.
"This is not a unique situation for Somalia. Cowards are trying to intimidate the Somali government but they will not stop us," he told the BBC's Focus on Africa programme.
Somalia has been devastated by civil war and anarchy for 14 years.
In May, at least 14 people were killed in a Mogadishu stadium where Mr Gedi was speaking on his first visit to the capital after his appointment.
Sunday's blast comes a day after Somali pirates attacked a US-owned cruise ship sailing off the east African country.
Crew members on the Seabourn Spirit repelled gunmen in speedboats who opened fire on the vessel, in an incident which terrified passengers.