Hundreds of militiamen loyal to Somalia's President Adullahi Yusuf have arrived in his temporary base of Jowhar, the government has confirmed.
Somalia remains in the grip of gunmen
This has prompted warlords in the capital, Mogadishu, to accuse him of plotting a military assault on them.
Somalia's transitional government has been split over its base leading to fears that this fourteenth peace attempt will crumble.
Meanwhile, the African Union (AU) has opened up an office in Jowhar.
The organisation's Said Djinnit confirmed this to the BBC on Thursday, but refused to give further details.
Somalia has been without a functioning national government for 14 years and a transitional parliament, sworn in a year ago, has failed to end the anarchy.
Led by the speaker of parliament, Sharif Hassan Sheikh Aden, more than 100 MPs have set up operations in Mogadishu, but President Yusuf refuses to return there saying it is unsafe.
The BBC's Mohammed Olad Hassan in Mogadishu says the capital has been tense since news of the militia movements emerged on Wednesday.
Rumours had already been spreading because Jowhar's phone lines were temporarily cut off.
The warlords and MPs warned aid workers and foreigners to leave Jowhar, 90km north of the capital, in a statement issued on Wednesday.
The troops in Jowhar include soldiers from Ethiopia - a long-time ally of the president, the statement said.
Government members, MPs and their allied armed groups in Mogadishu have been holding separate talks over the latest developments in Jowhar, our correspondent says.
"President Yusuf wants to wage a war against people in Mogadishu any time from now," National Security minister, Mohamed Khanyare Afrah told a Mogadishu radio station.
But Information Minister Mohamed Abdi Hayir in Jowhar denied there was any plan to invade.
The troops - which he said came from various areas of Somalia - were part of a reorganisation of armed forces to secure the government's base.
Mr Yusuf had said in July that he would recruit militia forces from his northern stronghold of Puntland to join a new army.
He has little support in Mogadishu and has refused to move there while it is still under the control of his rivals.
The Mogadishu warlords were named as ministers in Mr Yusuf's cabinet but soon fell out with him, siding with the parliament speaker.
Earlier they made threats to attack Jowhar if Mr Yusuf established the government there.