A local official said six other people were wounded in the gun battles that erupted in Marib, 170km from Sanaa, involving members of the Ubaida tribe.

Witnesses, however, said six people, including two police offices, had died and 16 were wounded during the firefights that began on Monday and continued until Tuesday morning.

They said the clashes broke out after security forces attempted to prevent the tribesmen from entering the town with their Kalashnikov rifles without a government permit.

The tribesmen managed to get into Marib and opened fire on government buildings, sparking exchanges of fire with police.

The battle ended only after the intervention of tribal notables.

Clashes involving tribes are common and often bloody in Yemen, a country with a tribal structure where the number of firearms in civilian hands is officially estimated at more than 60 million, or more than three for every inhabitant.