At least 800 al Qaeda militants, including some leaders, were killed in an attack on a southeastern provincial capital by the Yemen Army and the special forces of the United Arab Emirates and Saudi Arabia, the Arab coalition said in a statement on Monday. The coalition recaptured an oil well and Mukalla, a stronghold of the militant group, Agence France Presse quoted military sources as saying.

Almost 2,000 soldiers advanced on Sunday into Mukalla — a crucial seaport being used by the jihadist group to earn almost $2 million a day as customs revenues. The Arab coalition took over the port and airport, and set up checkpoints across the city, according to Reuters. Many al Qaeda fighters left the city, and air strikes killed 30 militants, Reuters quoted residents as saying, while the official press statement from the coalition pegged the militant death toll at over 800.

"Coalition armoured vehicles and the army entered Mukalla and al Qaeda fighters are departing," one resident told Reuters.

The Saudi Arabia-led coalition supports the President Abdrabuh Mansur Hadi government, which the group calls "legitimate," and is fighting to extricate cities fallen to the militant group, it said in a statement, according to the Saudi Press Agency. The group was also quoted by SPA as saying in the statement it retaking Yemeni cities from the militant group "will allow intensifying humanitarian relief efforts in those cities and alleviate suffering of the brotherly people of Yemen."

In Mukalla, air and ground operations took place in tandem, mostly by the UAE, which has been training local fighters for sometime, a Yemeni military official was quoted as saying by Reuters.

The restive country is embroiled in conflict with the Iran-backed Houthis, with whom the internationally recognised Yemen government has held talks about ending the civil war. U.S.-led air strikes and Arab coalition military operations, on the other hand, have been pounding the al Qaeda in the Arabian Peninsula (AQAP), which has formed a mini-empire in the south.