Two Ethiopian soldiers have been killed by a car bomb in the Somali town of Baidoa on Wednesday evening.
The bomber's target was an Ethiopian military post close to the hotel where the prime minister, Ali Mohamed Ghedi, was staying.
After the attack, Mogadishu-based Simba Radio aired an Islamist insurgent commander's claim of responsibility for the attempted assassination.
Somali forces have raided the radio and arrested its chief Abdullahi Ali Farak.
A reporter at the station said a journalist was also arrested in the raid, and the radio ordered to shut down.
A reporter at the scene says the area has been sealed off since the blast, but eyewitnesses say a suicide bomber driving a car also died.
"The explosion was so deafening and strong it rocked our entire hotel compound," an aide of the prime minister, Mohamed Abdi Haji, told AP news agency.
Mr Ghedi is in Baidoa for what correspondents expect to be a showdown between him and the president, Abdullahi Yusuf, on Friday.
More than 20 cabinet ministers have asked parliament to intervene on the simmering conflict between the president and prime minister.
The BBC's Mohamed Ibrahim Mualimu in Baidoa says the ministers who are allied to the president want parliament to vote on whether the government should be dissolved or not.
The two leaders have disagreed on whether the term of current transitional government which was formed in 2004 should end this Friday or in October 2009.
President Yusuf argues that constitutionally the government's term ends this month since it was formed three years ago, but his prime minister insists that the charter legalising their mandate was signed in 2006.
Parliament is expected to convene on Friday but its not clear whether the motion will be tabled.