The man was seized along with a Kenyan as they travelled in a car between the towns of Bu'aale and Saakow in the Juba region, the UN said.

Witnesses reported that gunmen fired at the car and abducted the workers, who were making a map of the area on behalf of the UN's Food and Agriculture Organisation (FAO).

Mohamed Mumin, said he saw six armed men shoot at the workers' car as it travelled along the road.

"I could see a white man running out of the vehicle with blood on his leg. I don't know whether he was injured or not," he said.

The two kidnapped workers were employed by an Indian company, Genesys International Corporation Ltd, which is under contract to provide an aerial survey for FAO.

An FAO spokeswoman in Rome confirmed two individuals were abducted by armed militia in Somalia and the FAO would be monitoring the situation closely.

A Foreign Office spokeswoman said officials were urgently investigating reports of the kidnap, but they had no further information.

Somalia has not had a functioning government since civil war broke out in 1991. UN aid helps millions of Somalians each year, but a number of foreign workers have been targeted by kidnappers and land mines in the past.

Britain does not have an embassy in Somalia, but officials in bordering countries are believed to be handling the situation.