An army jetfighter was downed by anti-aircraft guns near Arhab, 40 kilometres (26 miles) north of Sanaa on Wednesday, where armed tribesmen have been locked in combat with the elite Republican Guard, led by Ali Abdullah Saleh's son Ahmed.

"We saw the downed plane in flames on the ground," a witness said.

The plane crashed in the village of Beit Azar, and the pilot who had ejected was captured by tribesmen, witnesses and tribal sources said.

Heavy air strikes have targeted the tribal area of Arhab after a general and six other soldiers were killed Sunday in clashes between tribesmen and the Republican Guard.

General Abdullah al-Kulaibi, head of the 63rd brigade of the elite Republican Guard unit, was killed in the attack by tribesman opposed to Saleh's rule in the strategic town of Nihm, the defence ministry said.

Four of the attackers were killed during the attack on the military base, about 60 kilometres (40 miles) from the Yemeni capital, it said.

Meanwhile, three more gunmen were killed in overnight clashes with the guard, tribal sources said.

Nihm is one of several villages and towns that collectively make up the strategic northern gateway into Sanaa and is site of at least five Republican Guard bases.

The elite unit has so far prevented dissident General Ali Mohsen al-Ahmar, who now controls part of the capital, from calling in reinforcements from Yemen's northern provinces where parts of his division are deployed.

The tribesmen who carried out the assault on the military base late Sunday are allied with General Ahmar and have been battling government troops for control of the area.

Saleh, who is under international pressure to relinquish power and allow new elections, returned to the country last week, sparking violence in which scores have died.