The governor of Aden was killed in a car bomb attack on Sunday claimed by ISIS in Yemen's southern port city, where President Abd-Rabbu Mansour Hadi has returned to oversee a war against Iran-allied Houthis.

A local official and residents said at least six members of General Jaafar Mohammed Saad's entourage also died in the attack, which targeted the governor as he was headed to work. Several other people were wounded.

Yemenis inspect the scene of a car bomb attack that killed a Yemeni senior official in the southern port city of Aden, Yemen,on Sunday. STRINGER / EPA

ISIS, in a statement posted on a messaging service it uses, said it detonated a car laden with explosives aimed at Saad's convoy in Aden's Tawahi district and promised more operations against "the heads of apostasy in Yemen."

A local official and residents said earlier on Sunday a suicide bomber rammed his vehicle into the governor's car.

The group's local branch has stepped up operations since the outbreak of civil war in Yemen, emerging as a forceful rival to al Qaeda in the Arabian Peninsula (AQAP), the main militant group in the country in recent years.

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It has launched spectacular attacks on security bases and on mosques run by Houthi forces who control the capital, Sanaa. The Houthis, who follow the Zaydi branch of Shiite Islam, have been fighting a coalition of mainly Gulf Arab forces, which began air strikes against them in March.

The attack came one day after assailants killed a senior army officer and a judge who had presided over the trial of militants suspected in the bombing of the U.S. warship USS Cole in Aden in 2000, in two separate attacks in the city.

In October, four suicide bombers detonated car bombs at a temporary Yemeni government headquarters and two Arab coalition outposts, killing more than a dozen people.

"Foot-dragging in implementing security measures paves the way for hardliners to carry out such attacks," said Ashraf Ali Mahmoud, a local activist.