Yemeni soldiers patrol the city of Aden after taking it from AQAP militants on March 30, 2016. Photo via EPA

Yemeni and Emirati soldiers retook the Yemen seaport city of Mukalla on Sunday, the de facto capital of al-Qaeda in the Arab Peninsula (AQAP), as part of a major offensive to drive the group out of their southern strongholds.

The Saudi-led coalition claimed on Monday that at least 800 militants had been killed during the Mukalla offensive, though according to earlier reports the takeover was relatively peaceful.

"In its first hours, the operation resulted in killing more than 800 members of al-Qaeda and a number of their leaders while the rest fled," the coalition said in a statement carried by Saudi state news agency SPA late on Sunday.

Local Yemeni officials and residents said on Sunday that some 2,000 Yemeni and Emirati troops advanced into Mukalla, taking control of its maritime port and airport, and setting up checkpoints throughout the southern coastal city. They also said they had witnessed little fighting during the offensive.

Residents said local clerics and tribesmen had been in talks with AQAP earlier in the day to exit quietly and that fighters withdrew westward to neighboring Shabwa province. Air strikes killed 30 militants, residents said.

"We entered the city center and were met by no resistance from al-Qaeda militants who withdrew west," a Yemeni military officer told Middle East Eye.

Mukalla has been the center of a rich mini-state that AQAP built up over the past year as it took control of an almost 370-mile band of Arabian Sea coastline.

The group that has masterminded several foiled bomb plots on Western-bound airliners and claimed credit for the Charlie Hebdo magazine attack in Paris last year was pocketing around $2 million a day in customs revenues from the port.

Sunday's air strikes on al-Qaeda in Mukalla were carried out in coordination with a ground offensive in militant-controlled territory further west, a Yemeni military official said.

The push is being led by the United Arab Emirates, which has been training and arming local recruits for months, according to southern Yemeni tribal and political sources.

The UAE is part of a mostly Gulf Arab coalition that intervened in Yemen's civil war in March 2015 to support the internationally recognized government after it was forced into exile by the Houthi rebel group, which is an ally of Iran. Sunday's air strikes come as Yemen's government meets with the Houthis in Kuwait to try to find a solution to the conflict.

Around 6,200 people have died in the war, which has focused mostly around the country's Houthi-controlled center and north, while a security vacuum spread in the south. More than 3,000 of the dead are civilians, with the coalition accused of committing war crimes during its campaign, which has also created a major humanitarian crisis.

Since the beginning of the war, human rights organizations have documented more than 100 individual coalition airstrikes that could be in violation of international law, accounting for more than 1,000 deaths. [VICE News has compiled them into a single document, accessible here.]

Last month a British parliamentary committee announced that it planned to investigate allegations that weapons sold by UK firms to Saudi Arabia — last year, those sales totaled $4.2 billion — were being used to commit war crimes in Yemen. The European Parliament has called for the European Union to impose an arms embargo on the kingdom.

The United States has also been carrying out air strikes in Yemen for years, in the form of drone attacks — assisted by intelligence from Britain, VICE News revealed in an investigation earlier this month. Despite the group's gains in the last year, the US has managed to assassinate several of AQAP's top leaders, including its leader Nasser al-Wuhayshi, blown up on Mukalla's waterfront in June.

On Saturday, Yemeni troops also battled al-Qaeda at al-Koud near Zinjibar, another southern city considered an al-Qaeda stronghold, while an air strike from a drone killed two suspected two of the group's fighters south of the city of Marib.

In a statement on its official Twitter account, AQAP said it carried out a suicide bombing attack against the government troops pushing into al-Koud.

The Houthis control the capital Sanaa in the north while the Saudi-backed Yemeni government has tried to re-establish itself in the southern port city of Aden. Only in the last month has its fledgling army begun to make gains against the militants and organize to take back lost territory.

Watch the VICE News documentary: Seeking Refuge in Djibouti: Escape From _Yemen_**:**