A Houthi rebel mans a checkpoint amid fears of attacks by al Qaeda groups in Yemen in January 2015. (Photo by Yahya Arhab/EPA)

Al Qaeda has reportedly consolidated its control over a swath of southern Yemen by seizing Ahwar, a strategic coastal city in Abyan province that, along with its surrounding district, is home to more than 30,000 people

Residents of Ahwar said on Saturday that dozens of al Qaeda fighters had taken control of the city. Ahwar is an important geographic link between the major port city of Mukalla to the east and the smaller town of Zinjibar, both of which al Qaeda seized months ago.

"At dawn this morning the al Qaeda gunmen clashed with the Popular Resistance forces, killing three of them," one resident said. "They attacked the sheikh in charge of the area, and after he escaped set up street checkpoints and planted their black flag on government buildings."

Separately, two gunmen riding a motorbike killed one of the most senior commanders in the Popular Resistance, a loose confederation of southern militias opposed to al Qaeda.

Sheikh Mazen al-Aqrabi was killed along with a bodyguard in Yemen's second-largest city of Aden in the southwest, an eyewitness and a security official said. The gunmen were believed to be from al Qaeda, according to the official.

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Residents in Aden's Mansoura neighborhood also reported heavy explosions on Friday night as gunmen launched shoulder-fired rockets in a failed attempt to take over a container port.

Al Qaeda in the Arabian Peninsula (AQAP), a Sunni Muslim group that claims to be subordinate to the main global militant organization, has expanded during Yemen's civil war.

Viewed by Western analysts as the most dangerous arm of al Qaeda, it claimed responsibility for the deadly January 2015 attack in Paris on the satirical French magazine Charlie Hebdo.

AQAP's advance in Yemen has continued in the aftermath of a Saudi-led intervention in the country last March. The Saudis, who back the ousted government of President Abd-Rabbu Mansour Hadi, have clashed with Houthi rebels and their allies loyal to former strongman Ali Abdullah Saleh, while largely ignoring AQAP. Riyadh fears that the Houthis are a proxy for Shiite Muslim Iran, a claim that both the Houthis and Iran deny.

Hadi's Aden-based government has struggled to reverse AQAP's advance, which has reached areas close to the presidential palace.

Even so, AQAP has suffered setbacks, losing its leader and several top officials in US drone strikes, and is facing competition from the new Yemen branch of the Islamic State.