The Yemeni forces entered the city late yesterday, following days of heavy airstrikes by a Saudi-led coalition fighting on the side of President Abed Rabbo Mansour Hadi's government.
The airstrikes targeted al-Qaida positions in and outside Mukalla, the officials said, speaking on condition of anonymity because they were not authorised to talk to reporters.
Al-Qaida's local branch captured Mukalla last year amid the chaos caused by Yemen's civil war, which pits forces loyal to Hadi's government against Shiite rebels known as Houthis and their allies.
Troops loyal to Hadi also advanced over the weekend in the town of Koud in southern Abyan province, according to the province's governor, killing 25 militants from the group in heavy clashes. The coalition has also carried out airstrikes against al-Qaida positions in the area.
The pro-Hadi troops had been preparing for the offensive for months with the coalition's support. Heavy fighting is continuing with al-Qaida militants in Abyan, near the cities of Zinjibar and Jaar.