A top official in Somalia's Islamic militia said his forces would soon seize the base of the country's weak interim government, a move that would give radical militants uncontested authority over much of the country.
The government, which is internationally recognized but wields no real power outside its base in Baidoa, was on high alert, officials said.
"The Islamic Court, the ideology they are espousing is a very dangerous ideology -- they think they have the right to achieve things through violence, and that is dangerous," Deputy Prime Minister Ismail Hurreh said in demanding that the militia retreat.
The Supreme Islamic Courts Council militia seized Mogadishu last month and installed strict religious courts, sparking fears of a Taliban-style regime.
The US has accused the militia of links to al-Qaeda that include sheltering suspects in the 1998 bombings of US embassies in Kenya and Tanzania.
On Wednesday, more than 200 Islamic fighters seized the town of Bur Haqaba and were continuing toward Baidoa, 60km away, witnesses said.
The military movement came one day after the government started recruiting its own soldiers in central Somalia.
"Nothing will stop us from going into Baidoa," said Sheik Muqtar Robow, deputy defense chief for the Islamic group.
He gave no timetable for an attack, but said more than 130 fighters who were loyal to President Abdullahi Yusuf had defected to the Islamists' side.
"I call on remnants of Yusuf's clan forces to leave Baidoa peacefully," Robow said. "Anyone who wants to leave will not be harmed."
Another Islamic official denied fighters were planning to seize Baidoa.
"Our aim of going to the region is to convince people in the region to implement Islamic law and establish Islamic courts," said Mohamed Ibrahim Bilal, head of the local militia that seized control of Bur Haqaba.