Ethiopian forces are to start leaving Somalia "in the next few days", Prime Minister Meles Zenawi has told the BBC.
Mr Meles said the Ethiopians would withdraw in three phases
Ethiopia helped Somalia's interim government oust Islamists from the capital but has always said it does not want to stay long.
Mr Meles said the first phase of the withdrawal could start now that several key warlords had disarmed.
The African Union (AU) is meeting to discuss sending a peacekeeping force to Somalia to replace the Ethiopians.
The AU is considering a plan to send nine battalions of troops - some 8,000 men - with maritime, coastal and air support.
8,000-strong force proposed:
Uganda: 1,500 troops offered, subject to parliamentary approval
South Africa: Considering but forces stretched
Under the plan, three battalions would be deployed as soon as possible, with the rest within six months.
The plan warns that if the African peacekeepers are not deployed before the Ethiopian troops withdraw there is "a very high probability" of an Islamist resurgence.
It also calls for the UN to take over the peacekeeping force in the future.
Mr Meles would not guarantee his troops would remain in Somalia until AU peacekeepers had been deployed but said he thought there would be an overlap.
"We want to withdraw at the earliest possible opportunity but we want to do it in a responsible manner," he said, adding that the complete pullout would take place in three phases.
Mr Fall (l) urged President Yusuf to form an inclusive government
Uganda's ruling National Resistance Movement has approved plans to send some 1,500 peacekeepers to Somalia, meaning that parliament is almost certain to back the plans when it meets later this month.
No other country has made a public offer of troops, although the leaders of Ethiopia and Kenya on Tuesday said several unnamed African countries had offered to contribute troops to the proposed 8,000-strong force.
BBC African analyst Martin Plaut says it would take weeks for any troops to be deployed after a firm decision is taken.
He also says the real focus at the moment is on diplomacy, with US officials meeting Islamist leaders in Yemen, to discuss them joining the government.
The Somali government says some 3,500 Islamist fighters remain in hiding in Mogadishu.
Our correspondent says that unless the Islamists can be brought into the governing of their country, there is little prospect that any number of African or United Nations troops can bring peace to Somalia.
The US and the UN envoy to Somalia Francois Fall have both urged President Abdullahi Yusuf to form an inclusive government.
The 6,000-strong government forces are not seen as being capable of controlling the lawless country on their own - although it is being strengthened by the warlords.
Three of Somalia's major militia leaders have this week surrendered their weapons to the transitional government, while their fighters have joined the national army.
More than 60 "battle wagons" have been handed to the army
Omar Finish, Mohamed Qanyare Afrah and Musa Sudi Yalahow have surrendered control of more than 60 "battle wagons" - vehicles mounted with anti-aircraft guns - and some 380 fighters.
Four other warlords said their militias would disarm but they have not yet done so.
The former militiamen will now go to a military camp for training.
Their clan-based militias have battled for control of parts of Somalia for the past 16 years - since the country last had an effective national government.
The militias were hated by many Somalis for running road-blocks, where they extorted money.
On Thursday, Mr Fall urged the country not to waste "the best opportunity for peace for 16 years" after visiting interim President Yusuf in Mogadishu.
Mr Yusuf arrived in Mogadishu last week for the first time since being elected president at peace talks in 2004.