An Ethiopian soldier has been killed and another seriously wounded after unknown gunmen opened fire on troops at a market in Kismayo, southern Somalia.
Ethiopia has started to pull its troops out of Somalia
Somali army commander Abdulrazak Afgudud told the BBC that several people had been arrested.
The Ethiopian soldiers were on board a pick-up truck when the gunmen shot at them and escaped.
Ethiopia has begun a phased withdrawal of its troops from Somalia after helping the government oust Islamists.
The African Union is putting together a peacekeeping force to replace the Ethiopians.
AU chair Alpha Oumar Konare has appealed to countries across the continent to send peacekeepers to Somalia, saying there could be a "tragedy" without rapid intervention.
He said Ghana had agreed to supply troops, following Uganda, Malawi and Nigeria.
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
He was speaking ahead of next week's AU summit, at which the situation in Somalia is set to be high on the agenda.
In neighbouring Kenya, one of the main financial backers of the Union of Islamic Courts faces being sent back to Somalia, after pleading guilty to illegally entering Kenya.
A lawyer for Abubakar Omar Aden, a 72-year old businessman, who once controlled Somalia's El Maan port, said his life would be in danger if he was deported.
One of the UIC leaders, Sheikh Sharif Sheikh Ahmed, is also in Kenya, where he has held secret talks with US ambassador Michael Ranneberger.
Since the Islamists were removed from power in Mogadishu, Kenyan has closed its borders and deported dozens of Somalis who fled into the country.
The BBC's Mohammed Olad Hassan in Somalia says the Ethiopian soldiers were shopping at the time of the attack and were caught unawares.
"The gunmen used pistols and they have taken away AK-47 riffles from the Ethiopian soldiers," witness Abdullahi Hassan told the AP news agency.
Business premises at the market have been shut down following the attack - the first since Ethiopians and government troops took control of Kismayo earlier this month.
Some Islamists have pledged to conduct a guerrilla war against government forces. More than 3,000 Islamist gunmen are believed to have gone into hiding.
Kismayo was the last major town held by the Union of Islamic Courts to be taken by Somali government and Ethiopian forces.