Gunmen loyal to Yemen’s former president stormed a section of the international airport in the southern port city of Aden on Thursday, triggering heavy clashes with security troops who were firing back from armored vehicles positioned on the tarmac.

The fighting forced the closure of the facility and passengers on a flight to Cairo were scuttled off the plane and into the terminal building.

The attackers, loyal to longtime autocratic President Ali Abdullah Saleh who was ousted following a 2011 popular uprising, managed to enter a section of the airport grounds but were meeting with heavy resistance from the security forces loyal to current President Abed Rabbo Mansour Hadi, who is based in Aden.

As the fighting escalated, a convoy of tanks and armored vehicles was dispatched from the city center to the airport, less than a kilometer (half mile) away, security officials said.

More than 100 passengers who had boarded a flight to Cairo, including an Associated Press reporter, were ordered off the Yemenia aircraft and made their way to the terminal building as machinegun fire rang out. The plane was one of only two aircraft, both belonging to the national carrier, left on the tarmac.

The sound of heavy explosions shook the terminal building as the clashes intensified.

At least two shells have hit the airport’s grounds, said security and aviation officials at the scene, speaking on condition of anonymity because they were not authorized to talk to reporters.

Earlier, the fighting has centered around a security forces’ base adjacent to the airport’s eastern section. Saleh loyalists are led by renegade police Brig. Gen. Abdul-Hafez al-Saqqaf, according to the security officials.

If the airport in Aden, a major hub on the Arabian Sea, falls in the hands of Saleh loyalists, that would further isolate Hadi, who had declared the city as the country’s temporary capital last month after he escaped house arrest in the capital, Sanaa, at the hands of Iranian-backed Shiite rebels.

Beside the special security forces engaged in the airport clashes, two other army units in the city are also loyal to Saleh.

Yemen, the Arab world’s poorest nation, is deeply polarized and engulfed in turmoil that threatens to split the country amid a power grab by the rebels known as the Houthis.

The rebels last year seized Sanaa and several northern provinces, and in January declared themselves the country’s rulers. Hadi insists he remains the country’s legitimate leader and enjoys much support in Aden, where he has been based since fleeing house arrest.

Meanwhile, Yemen’s Al Qaeda branch, considered by Washington the terror network’s most dangerous offshoot, has profited from the turmoil and has been stepping up attacks on Yemeni forces and also the Shiite rebels.