People began streaming into the streets and setting fires just hours after the killing of Abdallah Isaaq Deerow, Somalia's minister for constitutional and federal affairs.
An unidentified gunman shot Deerow several times in the chest, then escaped, according to an Associated Press reporter at the scene.
"We condemn this wicked action and the government will chase the murderers and treat them with an iron hand," said the government's information minister, Mohamed Abdi Hayir.
The shooting was the second this week of a lawmaker in Baidoa, the only town controlled by the fragile administration. Mohammed Ibrahim Mohammed, chairman of the parliamentary committee for constitutional affairs, was wounded Wednesday night. Police were investigating both shootings.
The government, which has no military, has watched helplessly in recent months as Islamic militants have taken over the capital and much of southern Somalia. On Thursday, 18 top ministers resigned, saying the government has failed to bring peace to this chaotic African nation.
Deerow was not among those who resigned.
Also Friday, Islamic fighters closed roads around the capital's airport and chased away onlookers while a plane was unloaded. A similar aircraft delivered goods Wednesday, and officials from the government accused Eritrea of sending arms to the militants on that flight.
Islamic officials and Eritrea both denied the accusation. Eritrea and Ethiopia have been accused of supporting opposite sides in the Somali standoff, using the country as a battleground in their own rivalry.
The lawmakers who resigned Thursday said they were opposed to troops from neighboring Ethiopia who were sent here to protect the government from the Islamic group.
"We have seen that the government cannot carry out national reconciliation and development," said the resignation letter issued Thursday by 18 key ministers in the 102-member Cabinet.
Prime Minister Mohammed Ali Gedi accused the former Cabinet ministers of trying to bring down his government, but said it would not be affected.
The Islamic militants' increasing power has prompted grave concerns in the United States, which accuses the group of harboring Al Qaeda leaders responsible for deadly 1998 bombings at the U.S. embassies in Kenya and Tanzania. The Islamic group's imposition of strict religious courts also has raised fears of an emerging Taliban-style regime.