Fighters loyal to Somalia's Islamic courts have taken control of a key trading town from the transitional government without bloodshed.
Islamic court fighters took control of the capital Mogadishu in June
They drove into Sakow on Wednesday evening moving closer to the seat of the interim administration in Baidoa.
Islamists are reported to be massing to the east of Baidoa, where government troops have been seen building defences with the aid of Ethiopian soldiers.
The opposing sides are due to meet in Sudan next week for peace talks.
Somalia has been in the grip of warlords and militias for years and has not had a functioning national government since 1991.
The Union of Islamic Courts (UIC) has consolidated its control over much of southern Somalia after seizing the capital, Mogadishu, in June.
The UIC was set up by businessmen who wanted to impose law and order, and their gunmen have become Somalia's strongest fighting force.
"It was simple because we did not encounter any fighting when we entered the town," Sheikh Hassan Derow, an Islamist commander told AFP news agency.
Residents of the town which is 170km south-west of Baidoa, said pro-government forces fled to the north.
The BBC's East Africa correspondent Adam Mynott says the pressure is building towards a confrontation between the two sides.
But the UIC said it dids not intend to attack the transitional government but would defend itself against Ethiopian forces.
"The Courts' forces are still in their positions to defend the town (Baidoa) against the Ethiopian troops which began to move towards the Courts' forces," leading Islamic Courts offical Shaykh Sharif Shaykh Ahmad told the BBC.
Ethiopia has said that its only forces in Somalia are there for training purposes.
Eritrea, which is deeply hostile to Ethiopia, is also alleged to have sent troops to Somalia to reinforce the UIC.
Observers fear that Somalia could become engulfed in a wider war for control of the Horn of Africa.