Ethiopia is cutting its troop numbers in Somalia by about a third, Prime Minister Meles Zenawi has said.
About 200 Ethiopian soldiers left Mogadishu last Tuesday
He told Reuters news agency they would leave in the next 24 hours, but gave no precise details or numbers.
Thousands of Ethiopian soldiers were sent to help the weak Somali interim government oust Islamist forces.
Observers say a withdrawal makes the proposed African Union (AU) force to replace the Ethiopians an even more pressing issue at a summit on Monday.
The BBC's Amber Henshaw in Addis Ababa says some fear a political vacuum in Somalia, if there is no international support for the transitional government.
Our correspondent also says there is concern that there could be a re-emergence of the warlords who controlled much of the country since 1991 or an upsurge of violence from the Islamists.
Nine battalions proposed - up to 9,000 troops:
Uganda: 1,500 troops offered, subject to parliamentary approval
Malawi: Up to 1,000 troops offered
Nigeria: 1,000 troops offered
Ghana: Reportedly offered troops
South Africa: Considering but forces stretched
Ethiopia began pulling its troops out last Tuesday, with 200 seen leaving the capital Mogadishu.
"We are reducing troop numbers by about a third... that process should be completed today (Saturday) or tomorrow (Sunday)," Mr Meles told Reuters.
He declined to say how many troops had been sent to Ethiopia. Experts' estimates range from 5,000 to 15,000.
Mr Meles said he hoped to withdraw the rest of his troops "within weeks".
The proposed 7,600-strong AU force to replace the Ethiopians has drawn commitments from just three countries - Uganda, Malawi and Nigeria - although it is supposed to deploy by the end of the month.
In a separate development, the International Committee of the Red Cross has expressed concern about the deportation of Islamist suspects from Kenya to Somalia.
Spokesman Yazdi Pedram said there was no legal basis for repatriating them after they fled to Kenya during the recent fighting.
A second group of Islamists has been forcibly returned to Somalia - 23 prisoners arrived at Mogadishu international airport blind-folded, their legs in shackles, their hands tied behind their backs.
Heavily armed policemen escorted them onto trucks bound for an unknown destination.
Thirty-four suspected Islamists deported from Kenya a week ago are still in custody and have not been charged