TRIBAL fighters have entered the Yemeni coastal town of Mukalla in a bid to drive out suspected al-Qaeda fighters who took control on Thursday.

Residents said an alliance of tribal gunmen, who drove into the coastal town in pickup trucks on Saturday, has pledged to restore security after the Islamist militants drove the army out, ransacked buildings, broke into banks and freed prisoners from Mukalla's main jail.

In a statement, the tribal alliance said it intended to restore security.

It said: "The leadership of the tribal alliance of Hadramawt...calls on tribes to mobilise towards Mukalla to keep the peace and stability in Mukalla and other towns in the province."

The tribal alliance had already taken back control of the army bases in Shihr and Riyan in Yemen's eastern Hadramawt province, which had been abandoned by the army 48 hours earlier.

It was not immediately clear why troops had abandoned Shihr and Riyan, nor why they pulled out of Mukalla after offering relatively light resistance against the Islamist militants, but their withdrawal highlighted the further collapse of any central authority in Yemen.

That security vacuum may give al-Qaeda in the Arabian Peninsula (AQAP), a powerful regional wing of the global jihadi movement, opportunities to entrench itself further in the country's remote eastern reaches.

The United States, which has carried out covert drone strikes on suspected al-Qaeda targets in Yemen, withdrew its personnel from the country last month.

The Shi'ite Houthi forces, which seized the capital Sanaa six months ago along with soldiers loyal to former president Ali Abdullah Saleh, are fighting supporters of the current president in the southern port city of Aden.

Saudi Arabia and regional Sunni Muslim allies have waged 10 days of air strikes against the Houthis to try to stem their advances and to support President Abd-Rabbu Mansour Hadi, who fled Aden for Saudi Arabia more than a week ago.

Suspected al Qaeda fighters stormed Mukalla's prison on Thursday, freeing 150 detainees including a prominent local al Qaeda leader, Khaled Batarfi, Yemeni officials said.

They also broke into banks and set fire to the television broadcasting building, according to residents.