ADEN, Yemen - Forces loyal to Yemen's former president stormed the international airport in Aden on Thursday and sent fighter planes to bomb the palace in the southern port city where the current president has been based since fleeing from the rebel-held capital last month.

Troops fended off the airport attack, the airstrikes missed the palace, and President Abed Rabbo Mansour Hadi was in a safe place, Aden's governor, Abdel-Aziz bin Habtour, said.

But the violence, which he said had left 13 dead, marked a major escalation in Hadi's long-simmering conflict with former autocrat Ali Abdullah Saleh, who is allied with the Shiite rebels, known as Houthis. Hadi remains Yemen's internationally recognized president and has been a close U.S. ally in the battle against a powerful local al-Qaeda affiliate.

Thursday's attacks were led by forces loyal to Saleh, who stepped down in 2012 in the face of an Arab Spring uprising. A U.N. and Gulf-brokered deal saw Hadi, his vice president, assume office.

Saleh has never really conceded power, and Hadi has accused his predecessor of acting through well-placed loyalists to obstruct efforts to reform the government and security forces. The U.N. Security Council has sanctioned Saleh and top rebel leaders.

The Houthis swept down from their northern strongholds and seized the capital, Sanaa, in September. They now control at least nine of Yemen's 21 provinces. Hadi fled Sanaa last month after the Houthis put him under house arrest and he established a temporary capital in Aden, Yemen's main economic hub and the former capital of the once-independent south.

The assault on the airport set off clashes between forces loyal to Saleh and Hadi in Aden, with explosions echoing through the largely deserted streets. The warplanes then launched three airstrikes at Hadi's palace, on a rocky hill overlooking the Arabian Sea. The strikes caused no damage and Hadi was not present at the time, bin Habtour said.

It was not clear whether the planes were flown by Saleh loyalists in the military or by Houthi rebels, who control several military and air bases in and around Sanaa.

The attempt to capture Aden's airport appeared to be aimed at isolating Hadi and weakening his hold on the city. It is not yet clear if he will be able to leave Aden by the end of the month to attend an Arab Summit in Egypt. Officials said the airport was operating again, but there were no flights out Thursday evening.

Late Thursday, a statement issued by Hadi described the day's events as a "failed military coup against constitutional legitimacy."

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

During the fighting, more than 100 passengers - including an Associated Press reporter - were rushed off a Cairo-bound plane of the national carrier Yemenia that had been waiting on the tarmac and into the terminal building.

"One day it is the Houthis, another day it is al-Qaeda, and now Saleh's forces," a middle-aged man said as he looked out at the tarmac from the departure lounge. "We are getting it from all directions. We deserve some mercy."