Heavily-armed Islamist militia advanced closer to the seat of Somalia's interim administration on Wednesday, prompting the government to put its troops on alert against "aggression".
"If whatever we are hearing is true, and they are 35 km (22 miles) from Baidoa, then we consider this an act of aggression," Ibrahim Adan Hassan, minister of air and land transport, told Reuters from the government's provincial headquarters.
"The government troops are on high alert," he added.
The militia move inflamed already high tensions between the newly-powerful Islamists and the government, which many Somalis fear could boil over into an all-out fight for supremacy in the Horn of Africa nation of 10 million.
Somalia has been without central rule since the ouster of a military dictator in 1991, and the Islamists' recent take-over of the capital Mogadishu has threatened the aspirations of President Abdullahi Yusuf's Western-backed interim government.
Yusuf was not in Baidoa but his home region and stronghold Puntland on Wednesday, government sources said.
Islamist militiamen, riding on heavily-armed pickup trucks known as "technicals", arrived in Buur Hakaba in the morning, the closest they have come to Baidoa since capturing Mogadishu from US-backed warlords last month.
Islamist officials said their militia had travelled from the capital to receive 150 government troops switching allegiance to the newly powerful Islamist movement. Whether had gone beyond Buur Hakaba, on the road to Baidoa, or were pulling back to Mogadishu could not be independently confirmed.
"It's true that 150 government forces have joined the Islamic courts. I am with them and I'm bringing them to Mogadishu," Sheikh Mukhtar Robow, a senior Islamic official in charge of defence, told Reuters.
Residents in Buur Hakaba town said the militiamen arrived in a convoy of more than 20 technicals, Somalia's version of tanks.
"50:50 CHANCE OF WAR": Minister Hassan said the government had received reports the Islamic fighters had reached Buur Hakaba. "We still don't know why they are there," he told Reuters, denying that any government troops had switched sides.
The move came two days after the Islamists opened a sharia court in the government-controlled Bakol and Bay area, where Baidoa is located. It was the first time they set up a court in an area they do not yet control since taking Mogadishu.
One expert predicted a 50:50 chance of conflict in Somalia in coming weeks. He cited Islamist military expansion, an attack by gunmen loyal to Yusuf on Mogadishu, or intervention by Yusuf's powerful ally, Ethiopia, as possible triggers.
Up to 2,000 Ethiopian troops crossed the border last week with several tanks to join about 2,000 soldiers already there, various sources said.
"If the Ethiopians fight alongside the government, the Islamists will mobilise more support from the population," said the Nairobi-based analyst, who declined to be named. "Yusuf is using the Ethiopians as a threat...If he really thought that he could win, he would have gone in two weeks ago."