Unknown assailants shot dead the Somali head of the United Nations Development Programme (UNDP) late on Sunday as he was on his way home from saying evening prayers in the chaotic capital Mogadishu, witnesses said.

Osman Ali Ahmed, head of the UNDP office in Mogadishu, was shot six times in the head, ribs and stomach from close range by men armed with pistols. His younger brother was fatally wounded.

"He was already dead on arrival," an official at the Ugandan soldier's medical facility in Mogadishu told Reuters, declining to be named. "His bed and his body was covered with blood. He died of loss of blood."

Anarchic Mogadishu is one of the most dangerous cities in the world especially for aid workers and foreign journalists. Somalia has had no central rule since the 1991 ouster of a dictator.

Insurgents are waging a battle against the interim government, and have adopted Iraq-style tactics including bombings and assassinations of government offices, aid workers and intellectuals.