At least 26 people have been killed in clashes between Ethiopian forces and anti-government fighters in central Somalia, residents have said.

The Somali opposition fighters ambushed an Ethiopian army convoy travelling from Guguriel near the Ethiopian border to Mataban, about 450km north of the capital Mogadishu, they said.

"I counted 18 bodies in and around Mataban town," Hussein Moaliam Aden, an elder in Mataban, said.

Aden said that he had seen the bodies of at least seven Ethiopian soldiers lying near the site of the ambush.

Mataban residents said that a child was killed as the fighting spread into the town, they said that 26 people had been killed.

"One child was killed in the crossfire in Mataban," Mohamed Hadi Ali, a resident, said.

The fighting was the heaviest in the region since Ethiopian forces entered Somalia in late 2006 to support the country's weak government, residents said.

Aid workers captured

In a separate development, a Somali official said on Tuesday that armed men have captured four local aid workers outside the capital.

A woman and three men working for the Italian non-governmental organisation Water for Life were kidnapped from their car on Monday, Abdulqadir Sheik Mohamed, a governor in the Lower Shabelle region, said.

The aid workers were captured on the same day that a Somali aid worker was shot dead in Mogadishu, according to a UN official.

Siyad Orow, 38, head of Asal, a local Somali charity, was kidnapped and later shot dead, the UN official said on condition of anonymity.

Family member Mohamed Mo'alim Yusuf confirmed that two men killed Orow in Bakara, but gave no other details on the identity of the attackers.

Asal is a charity that works with the World Food Programme (WFP) to distribute food to hundreds of thousands of Somalis camped along the road between Mogadishu and Afgoyee, 30km to the west.