SANAA: Gunmen loyal to Yemen's ousted president blasted buildings at the country's main airport with anti-aircraft guns on Saturday, forcing authorities to shut it down, an airport official said.

Armed tribesmen and troops in uniform driving pickup trucks mounted with heavy weapons opened fire on a tower and destroyed it, he said. Then they surrounded the airport at the capital Sanaa, cut roads and sent passengers' vehicles away. Authorities canceled flights, the official said.

The attack comes a day after Yemen's new President Abed Rabbo Mansour Hadi fired key security officials appointed by ex-president Ali Abdullah Saleh including his half brother, the air force commander Mohammed Saleh al-Ahmar, and his nephew, Tariq, who headed the presidential guard.

The siege of the airport highlights the challenges faced by Hadi, who has pledged to purge Saleh's loyalists from the army, the security apparatus and key government posts.

Saleh stepped down in February following a year-long uprising in which huge crowds rallied in city squares demanding an end to more than three decades of his authoritarian rule. After many false starts and reversals, he finally in November signed a power-transfer deal backed by Washington and Gulf Arab states that gave him immunity from prosecution.

Critics of the deal say it gave Saleh the ability to act as a president from behind the scenes and plot his comeback, possibly by sewing instability.

On Thursday, Yemeni Defense Minister Mohammed Nasser Ahmed told parliament that Saleh is still giving orders to governors and security officials using headquarters of his son, Ahmed — the commander of the powerful Republican Guards— as his operation room.

Saleh's opponents are particularly worried about his loyalists who command military units. The army has recently suffered several defeats in its war against al-Qaida-linked militants who took control of several towns in the south of the country, and many believe that Saleh commanders may be actively sabotaging the campaign.

The airport attack suggests that removing the commanders comes with its own set of dangers — if it is even possible.

Aides to sacked air force commander Mohammed Saleh al-Ahmar who held his post for more than 20 years say he will remain in the position and will not follow orders until Hadi also fires some of the ex-president's opponents. His replacement is former Air Force commander Rashid al-Hanad.

They referred to Gen. Ali Mohsen al-Ahmar, who defected last year to the mass uprising that called for Saleh's ouster and brought his First Armored Division to protect protesters.

Also on Friday, Hadi sacked longtime Saleh loyalist Mohammed Ali Mohsen, the head of the Military's Eastern Command, which is responsible for areas where al-Qaida is active. He was transferred to an administrative post.

The changes however didn't touch ex-president's son Ahmed who kept command of the well-equipped Republican Guard, or his nephew, Yahia, the head of the Central Security Forces.

On Tuesday, Saleh's son carried internal reshuffles of his own, including appointing the now-ousted presidential guards' commander Tariq Saleh as a commander of one of the biggest brigades in the Republican Guards. The appointments were reported by state TV even though Hadi's aides said the president had never approved them.

Officials spoke on condition of anonymity because they are not authorized to speak to the press. AGENCIES