A military official said the plane, a Russian-made Sukhoi fighter, had been shot down while conducting a routine mission.

The tribal source said fighters shot down the plane using anti-aircraft weapons and detained the pilot when he jumped from the wreckage in the mountainous area of Naham.

Some tribes have aligned with protesters seeking to oust President Ali Abdullah Saleh, who unexpectedly returned to Yemen last week from Saudi Arabia during a wave of violence in the capital that left more than 100 people dead.

Earlier this week, tribesmen attacked a military base in Naham, stealing arms and killing a general. Three tribesmen were also killed in the fighting.

International powers fear instability in Yemen could create a wider security threat.