Witness Fadhel Mubarek said law and order broke down in the city after government troops fled for their lives. Armed gangs looted banks and all government facilities.

Hundreds of families are leaving the city despite militant assurances that they mean no harm to the civilian population and their aim is to establish an Islamic state, Mubarek said.

After withdrawing from the city, Yemeni troops shelled it with tanks and heavy guns. The militants responded by firing rocket-propelled grenades.

“Bodies of dead soldiers are in the streets and no one is able to remove them due to heavy shelling. Residents are trapped in their houses without water and electricity in extremely hot weather," Mubarek said.

Another witness said the militants were combing the city in search of security officials to settle scores.

Opponents of the country's embattled president, Ali Abdullah Saleh, accused him of allowing the militants to freely seize Zinjibar in a bid to stoke Western fears that Al-Qaeda would take over the country if he responded to demands by demonstrators to step down.

In another development, a brigade of the powerful Republican Guard has defected to the opposition in a southern province. Activist Abdul-Rahman Ahmed said a letter from Brig. Gen. Ibrahim Al-Jayfi, commander of the Guard's Ninth Brigade, was read to thousands of protesters in the provincial capital of Damar on Sunday.

Sheikh Sadeq Al-Ahmar of the powerful Hashid tribal confederation, whose fighters battled Saleh's troops for five days last week, has called on the Republican Guard to help topple Saleh.

In the capital Sanaa, a truce between the government forces and tribesmen loyal to Al-Ahmar held. "Today we agreed to hand over the Ministry of Local Administration to tribal mediators as a gesture of good will and to prevent more bloodshed. We still control the Ministries of Industry, Endowment and Tourism," Abdul Qawi Al-Qaisi, spokesman for Al-Ahmar, told Arab News.

Al-Qaisi accused Saleh's forces of taking advantage of the truce to deploy more troops in the Hasaba district.

In Hadramaut province, security forces were searching for three French citizens who went missing Saturday in the city of Seiyun.