SANAA, Yemen — Al-Qaida militants traveling in convoys flying black banners captured a major port city in southern Yemen on Thursday, seizing government buildings and freeing inmates from a prison, including a top Saudi-born leader, security officials said.
The fall of Mukalla — the capital of Yemen's largest province, Hadramawt — highlighted how al-Qaida is expanding its foothold in Yemen, taking advantage of the turmoil as a Saudi-led coalition backing the country's beleaguered president tries to fend off a takeover by Shiite rebels.
Mukalla's fall came as the rebels, known as Houthis, made dramatic advances in one of the main strongholds of the president's loyalists, the southern city of Aden. The rebels broke into the center of Aden and briefly captured a presidential palace in the city.
The rebels withdrew from the palace after raising the Yemeni flag, but the move showed their continued strength despite more than a week of heavy airstrikes by the Saudi-led coalition. If the Houthis succeed in capturing Aden, it would be a significant blow to the coalition, which has been planning to land ground troops in the city to allow the return of President Abed Rabbo Mansour Hadi, who fled the country last week.
At least 519 people have been killed, many of them civilians and 90 of them children, in the past two weeks of violence in Yemen, as well as 1,700 wounded, the U.N. humanitarian chief Valerie Amos said. She said tens of thousands have also fled their homes.
Al-Qaida in the Arabian Peninsula, as the terror network's branch in Yemen is named, has been benefiting from the turmoil ever since the Houthis first surged from their northern strongholds last year to take over the capital, Sanaa, and much of the north. The rebels are backed in the campaign by military and police forces loyal to Hadi's predecessor, ousted autocrat Ali Abdullah Saleh.
Around the country, some Sunni tribal fighters have been making alliances with al-Qaida to fight the rebels, who adhere to the Zaydi branch of Shia Islam.
But the capture of Mukalla was a startling advance. The city lies 300 miles northeast of Aden along the Arabian Sea coast in large but sparsely populated Hadramawt.
The militants fanned out along major roads leading into Mukalla on Thursday and took over the city's presidential palace, government agencies and the local Central Bank branch. They tried to break open the bank's vault with hand grenades but failed, according to witnesses. The witnesses spoke to The Associated Press on condition of anonymity for fear of reprisals.
Militants on pickup trucks set up checkpoints across the city, sealing off entrances and exits, while residents were seen entering the offices and looting electronic devices and files, the witnesses said.
The al-Qaida fighters also freed about 300 inmates from the city's main prison, including scores of militants, according to security officials.
Among those freed was Saudi-born Khaled Batrafi, a senior al-Qaida operative believed to have masterminded past attacks, the officials said.
Also freed were 90 death row inmates convicted for a host of criminal offences, according to activists in the city.
After the noon prayers, a top al-Qaida leader stood up in the middle of the worshippers in the city's al-Sharag mosque, telling them that he and fellow militants were there only to defend the city from the Houthis.
"People are terrified," said Ali al-Katheri, an activist in Mukalla. "They never expected that the city falls so easy in hands of al-Qaida."
Police commandos in the city were loyal to Saleh, the former president, and did not resist the al-Qaida advance. Army units loyal to Hadi are stationed in bases on the city's outskirts but also did not move against the militants, apparently too weak to fight back. At one point, a military helicopter opened fire on the militants but withdrew after hitting residential homes, al-Katheri said.
Al-Qaida in the Arabian Peninsula is seen by Washington as the terror network's most dangerous branch ever since its attempt in 2009 to bomb a commercial carrier over the United States. It claimed responsibility for January's deadly attack in Paris on the French satirical weekly Charlie Hebdo.
The rebels' power grab, combined with nationwide chaos, has forced the United States to pull out military advisers who were backing the Yemeni military against al-Qaida, undermining U.S. counter-terrorism operations and drone strikes.
The air campaign by Saudi Arabia and its Arab allies has been pounding Houthi and pro-Saleh forces in Sanaa and multiple provinces around the country. In recent days, the warplanes have been hitting hard in Aden, trying to fend off the rebels and Saleh's troops amid fierce fighting with Hadi's loyalists on the ground.
Airstrikes in Aden on Thursday hit a base of pro-Saleh police commandos and a hotel being used by Houthi fighters, killing at least 20 people, Yemeni security officials said. The officials spoke on condition of anonymity because they weren't authorized to talk to the press.
Hadi's loyalists have held the city's center, located on a peninsula jutting into the Arabian Sea, while their opponents held the airport at the base of the peninsula and some neighborhoods to the north.
But on Thursday, Houthi fighters were able to break into the city center, driving through the commercial district, seizing several neighborhoods and capturing the presidential palace at the peninsula's tip. They held the palace as a "show of strength" before withdrawing for fear of airstrikes, the security officials said.
Fighting still raged in the evening as Hadi's forces and loyalists held onto scattered parts of the city, and airstrikes battered the airport.
Warplanes also struck an island in the strategic Bab al-Mandab strait, the southern entrance to the Red Sea, after Houthis took over the island earlier Thursday, officials said.
Saudi and Egyptian warships deployed to Bab al-Mandab which gives the only access to Egypt's Suez Canal from the Arabian Sea and is a vital passage for shipping between Europe and Asia.
Saudi Arabia, meanwhile, said one of its guards along the border with Yemen was killed Wednesday night. It was the first known Saudi casualty since the airstrikes started.
A border post in the Asir region came under heavy fire from a mountainous area inside Yemen, followed by cross-border skirmishes, according to the official Saudi Press Agency. Along with the Saudi guard who was killed, 10 other border guards were wounded, SPA said.