* Briton, Frenchman worked as consultants for UN drug agency
* Pair were shot by man in police uniform, local resident says
* U.N. staff previously targeted by Islamist group al Shabaab (Adds nationalities of victims, Shabaab reaction)
By Abdiqani Hassan
BOSASSO, April 7 (Reuters) - A Briton and a Frenchman working for the United Nations were shot dead on Monday at an airport in north central Somalia, officials said.
A U.N. mission spokesman said it was not clear who was behind the killings. But one witness said the pair were attacked by a man in a police uniform while they sat in their car at Galkayo airport.
Abdi Idris, an official in the semi-autonomous Puntland region which administers the airport, gave the nationalities of the two men and said they worked as consultants for the UN anti-drugs agency.
The U.N., which has spent billions of dollars in Somalia since the outbreak of civil war in 1991, has often been targeted by warring clan factions, most recently by Al Qaeda-aligned Islamist group al Shabaab.
Somalia's Puntland regional has traditionally been more stable than the rest of the country but in recent months attacks there by al Shabaab militants have increased.
The Islamist group "welcomed the killing" but declined to comment when asked if it was responsible. "We urge all Somalis to target the U.N.," a spokesman for the group, Ali Mohamud Rage, told Reuters.
Local resident Cali Faratol, who was at Galkayo airport when the workers were attacked, sad a man wearing a police uniform shot them.
"Both men were in a car when he was shooting," Faratol said.
Nicholas Kay, the U.N. Special Representative for Somalia, condemned the "callous" killing but said the organisation remained "committed to continuing our vital support to the Somali people as they emerge from decades of conflict."
Al Shabaab gunmen in the capital Mogadishu used a car bomb to blow a hole in the U.N. compound's wall last June and 22 people, including U.N. staff, were killed in the ensuing firefight.
In February this year al Shabaab attacked a U.N. convoy with a remote-controlled bomb, killing at least seven Somalis. No U.N. staff were hurt in that attack. (Additional Reporting and Writing by Drazen Jorgic; Editing by James Macharia, John Stonestreet)