The governor of Aden was killed by a car bomb on Sunday in Yemen's southern port city, in an attack that Islamic State claimed responsibility for.

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 on his way to work. Several other people were wounded.

The attack came in the Tawahi district of Aden, where President Abd-Rabbu Mansour Hadi has returned to oversee a war against Iran-allied Houthis.

Islamic State, in a statement posted on a messaging service, said it detonated a car laden with explosives as Saad's convoy passed by. The group promised more operations against "the heads of apostasy in Yemen".

The group also posted what it said were photos of the booby-trapped vehicle as a white van carrying Saad drove past, then two other photos of a huge ball of fire which it said were taken as the bomb exploded.

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

Islamic State'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.

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

The attack came a 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.

Sunday's explosion could be heard about 10 km away, residents said. Photos posted by local news websites showed a car in flames with a plume of smoke rising from it.

The victims were taken to the Jumhouriya Hospital, the main state medical facility in Aden which Saad had re-opened in a ceremony two days earlier.

Medics said the body of Saad and the others who were killed were burned beyond recognition.

Security had been a main concern for Hadi and his Arab allies since he returned to Aden last month to oversee an offensive by his forces and Arab allies to drive the Houthis from the strategic city of Taiz.

In October, the government of Prime Minister Khaled Bahah was forced to relocate to Saudi Arabia after four coordinated suicide bombings by Islamic State killed at least 15 people, including four Emirati soldiers.

Saad had been a general in the army of the former southern Yemen before the Marxist state merged with northern Yemen in 1990. He was appointed governor in October.

Local officials said Saad, who fought in the 1994 civil war for southern forces against the northerners, had lived in exile in Egypt and Britain before he returned earlier this year at Hadi's request.

In a separate incident, residents said a field commander of a local militia group that had helped drive the Houthis out of Aden in July was shot and killed by unknown assailants in the west of the city on Sunday.

It was not immediately clear if that attack was linked to Islamists or if it was a result of the general lawlessness gripping Aden.-Reuters