Yemeni government troops fought their way into the center of an al-Qaida-held city in the lawless south after a fierce, six-hour battle that ended early Tuesday, military officials said.

FBI director Robert Mueller held talks with Yemen's new president on the fight against al-Qaida militants, particularly in southern Abyan province where the earlier battle raged in the town of Zinjibar.

Al-Qaida militants seized Zinjibar, the provincial capital of Abyan, last May when fighters from the terror network's Yemeni branch took advantage of the internal political turmoil in the impoverished nation to capture several cities and towns in the south.

The latest fighting is part of a stepped up efforts by government forces in their fight against al-Qaida. President Abed Rabo Mansour has vowed to make the fight against the terror network a priority.

Mueller met Hadi for 45 minutes in the capital Sanaa, said Hadi's spokesman Yahya al-Arasi. He said the two men discussed political support for Hadi, who took over two months ago from longtime authoritarian leader Ali Abdullah Saleh. Hadi, according to al-Arasi, stressed to Mueller the importance of U.S support for the campaign against al-Qaida.

The FBI is the U.S. government's main domestic law enforcement agency, but it has liaison offices in countries around the world.

Mueller's unannounced visit came hours after news that government forces fought their way into the center of Zinjibar.

The United States says al-Qaida's Yemen branch is the terror network's most dangerous. The U.S. has over the years provided millions of dollars for equipment and training to improve the capabilities of the Yemeni forces.

In a separate development, Saleh's half brother, air force commander Mohammed Saleh al-Ahmar, finally gave up his command Tuesday and left his office at the military section of the international airport at Sanaa. Al-Ahmar had previously rejected Hadi's decision to replace him and refused to leave.

Al-Ahmar's dismissal from his longtime command of the air force was part of Hadi's shake-up of the armed forces, weeding out Saleh loyalists and relatives from key posts.

The U.S. ambassador to Yemen, Gerald Feierstein, said over the weekend that the shake-up has helped the fight against al-Qaida.