Forces loyal to Yemen's former president stormed the international airport in the southern port city of Aden on Thursday, triggering an intense, hours-long gunbattle before security forces loyal to the current president repelled them.

The fighting forced the airport's closure, and passengers on a flight to Cairo on the tarmac were rushed off the plane and into the terminal building. Sporadic clashes between the two sides' loyalists erupted around Aden, the country's second most important city and economic hub, overlooking the Arabian Sea.

The assault in Aden was the latest against Yemen's embattled, internationally backed president, Abed Rabbo Mansour Hadi, who was driven out of the capital, Sanaa, after a takeover by Shiite rebels known as Houthis. Hadi and his allies fled to Aden, which they have made their de facto capital in a conflict that threatens to push the long unstable, impoverished nation into outright fragmentation.

The attack on the airport was by forces loyal to Ali Abdullah Saleh, the longtime autocratic president who was ousted from power by a 2011 popular uprising. Saleh has allied with the Houthis against Hadi, and his loyalists still command parts of the military and police. The attempt to capture Aden's airport appeared to be aimed at isolating the city and weakening Hadi's hold.

Last week, Saleh boasted he would corner Hadi as he fled from Sanaa. "Those fleeing to the south ... will find only one exit: the Red Sea toward Djibouti," he said in a speech to his supporters.

Tensions have been building for days in Aden. Hadi's loyalists, in the military and police and in militias known as Popular Committees, dominate the city. But two army units in the city are loyal to Saleh, as is a force of 3,000 police special forces under a pro-Saleh commander, Brig. Gen. Abdul-Hafez al-Saqqaf. Hadi tried unsuccessfully to remove al-Saqqaf from his post earlier this month, prompting some clashes.

The fighting started in the early hours Thursday when a unit of al-Saqqaf's police special forces stormed the airport grounds, sparking heavy battles with pro-Hadi forces. Machinegun fire rang out and explosions shook the terminal building.

At least two shells hit the airport's grounds, said security and aviation officials at the scene. Three of Saleh's loyalists were killed and 10 were captured in the clashes, according to security and medical officials.

During the fighting, more than 100 passengers — including an Associated Press reporter — were rushed off a plane of the national carrier Yemenia that was on the tarmac, preparing to head to Cairo, They were rushed into the terminal building.

One of Hadi's presidential planes, a Boeing 747, was damaged when Saleh loyalists sprayed it with gunfire, the officials said. All officials spoke on condition of anonymity because they were not authorized to talk to reporters.

During more than four hours of fighting, a convoy of tanks and armored vehicles, led by Hadi loyalist Defense Minister Maj. Gen. Mahmoud al-Subaihi, arrived from downtown Aden to reinforce the airport's defenders. Al-Subaihi's troops then ordered passengers out of the terminal and the airport building, through the thick of the clashes.

Al-Subaihi's troops succeeded in taking back control of the airport. They then turned to the adjacent base of the pro-Saleh police commandos, surrounding it and pounding it with artillery, before trying to storm it in the afternoon, prompting heavy clashes, officials said.

Sporadic clashes also erupted throughout Aden between Saleh and Hadi loyalists. Sounds of explosions periodically shook the city, and streets were largely deserted as residents hid in homes.

Armored vehicles and tanks fanned out into the streets, and fighters from Hadi's Public Committee militias roamed the city in pick-up trucks mounted with heavy machine guns. They and pro-Hadi security forces deployed around hotels and government buildings and the Central Bank building. Saleh's forces took control of the local city council building, and ambulance sirens could be heard across the city.

Yemen, the Arab world's poorest nation, is deeply polarized and engulfed in turmoil that threatens to split the country amid the power grab by 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 and al-Sabaihi fled after several weeks under house arrest in the capital, Sanaa.

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.

The group claimed responsibility for the assassination of a prominent Houthi supporter and politician, Abdel-Karim al-Khewani, who was gunned down in front of his house in Sanaa.