Heavily armed militants from the al Shabaab group also attacked the homes of government officials in Baladwayne, a small town near the Ethiopian border.

"We are terrified because people who were involved in educating us were killed," said one local man, Nur Muse.

It was just the latest in a string of hit-and-run raids by rebels who have stopped a Western-backed interim government asserting its authority on the chaotic Horn of Africa country.

The militants, who are listed by Washington as a terrorist group with ties to al Qaeda, had left Baladwayne by morning.

Residents said the two Britons, who were both ethnically Somali, left their homes in Britain a year ago to build the school in the remote town.

Abdihakim Mahamud, a nephew of the dead man, identified him as Daud Hassan Ali. He said his uncle's friend, Rehena Ahmed, had been in her 20s. She was shot in the head, while Ali and the two Kenyan men were shot in the chest.

"Their bodies are lying at the hospital," Mahamud said.

"CROSSFIRE"

A senior commander of the al Shabaab, Mukhtar Ali Robow, said the four victims were killed accidentally in crossfire.

"Our motive was not to kill innocent people," he told Reuters by telephone from an undisclosed location. "Their guards shot at us and we had to fire back."

The al Shabaab is the militant wing of a sharia courts group that ruled most of southern Somalia for the second half of 2006.

It is now at the forefront of an Iraq-style insurgency of ambushes, roadside bombings and assassinations targeting President Abdullahi Yusuf's government and its Ethiopian allies.

Robow said his fighters had launched more attacks overnight in the capital Mogadishu, which has suffered most of the violence, including firing rockets at Burundian peacekeepers.

He said the rebels had also seized a pick-up truck mounted with an anti-aircraft gun during an assault on a police station.

A spokesman for the Burundian troops, who are part of a small African Union peacekeeping force, confirmed that a base at a former university had come under fire, but gave no details.

Analysts say al Shabaab's tactics are to stretch Yusuf's fragile administration, while avoiding face to face fighting with the well-equipped Ethiopian forces that are supporting it.

Clashes killed 6,500 people last year in the coastal capital and uprooted hundreds of thousands. Aid agencies say the 250,000 civilians camped just outside Mogadishu are now considered the biggest group of internally displaced people in the world.