Somalia's interim government has asked for international help in investigating Monday's failed assassination attempt on President Abdullahi Yusuf.
A government spokesman says police need foreign expertise in their probe of what is believed to be Somalia's first suicide bombing.
Five people including the president's brother were killed Monday when a car bomber rammed the presidential convoy.
Security guards killed six suspected assailants in a gunbattle after the blast.
The attack took place in Baidoa, the only town the weak interim government controls.
There has been no claim of responsibility for the blast, which government officials blame on al-Qaida or Islamists who control the capital, Mogadishu.
Islamist leaders in the capital have denied any involvement in the attack. They blame Ethiopia's government, saying officials there want to create a pretext for deploying peacekeepers to Somalia.
Somalia's U.N.-backed interim government and the Islamists are attempting to work out a peace agreement. But talks have been deadlocked over the issue of a regional peacekeeping force in Somalia, which the Islamists strongly oppose.
Witnesses say the interim government has stepped up security in Baidoa Tuesday, with police stopping cars at checkpoints around government buildings.Some information for this report was provided by AFP, Reuters.