SANAA: Fighters loyal to tribal chief Sheikh Sadiq al-Ahmar, who heads a coalition backing anti-regime protests, clashed with army troops in the Yemeni capital on Friday, witnesses said.
Loud explosions and gunfire rocked the Al-Hassaba district of Sanaa.
Witnesses said an armoured vehicle of the elite Republican Guard, which is led by President Ali Abdullah Saleh's son, Ahmed, was hit by a projectile and set ablaze.
There were no immediate casualty figures available.
The troops earlier blocked several roads and erected checkpoints, triggering a similar action by the tribesmen armed with machine guns and rocket-propelled grenades.
Fierce clashes between Ahmar's tribesmen and loyal troops in Al-Hassaba in May killed more than 140 people before the two sides agreed a truce.
The sheikh heads the powerful Hashid tribe which ended its support to Saleh - also a member of Hashid - in March and joined the protests which erupted in January demanding the ouster of the president.
Influential tribal leaders formed last week a coalition headed by Ahmar to bolster the uprising against Saleh who has been in a Saudi hospital since June after being wounded in a bomb attack on his Sanaa compound.
Tribes wield much influence in impoverished Yemen, where the Hashid is a heavily armed tribal confederation capable of rallying and financing thousands of fighters. The Bakil is the other main tribal confederation.
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