Colonel Abdullah al-Mouzai, the head of the police in Aden, "was killed when a device placed in his car exploded," the police official said, adding that the blast occurred when the police chief left home for his office.

A medic told AFP that Mouzai was "seriously injured and taken to the hospital where he succumbed to his wounds."

The police official blamed Al-Qaeda for the attack.

"Al-Qaeda elements placed the explosives in the colonel's car," he said, adding that Mouzai had previously survived four assassination attempts in Aden as well as in the neighbouring Lahij province where he used to work.

The official further said that security forces had "dismantled four explosive devices placed in vehicles of police officers across Aden since the beginning of July."

In a separate incident in Aden, a gunman was injured when he threw two bombs early Thursday at the local administration's headquarters, a security official said.

"He threw a bomb that fell into the compound, while a second bomb hit the outer wall and bounced back on the assailant wounding him," the security official said, without giving any details of the attacker.

There were no reports of other casualties in the incident.

Al-Qaeda militants had strengthened their presence over the past year across the south, taking advantage of a central government weakened by an Arab Spring-inspired uprising.

But on May 12, the military launched an all-out offensive against them, making significant advances.

Aden is also a stronghold of the Southern Movement that groups activists pushing for greater autonomy for the south and those who want full independence for the region, which was a separate state until 1990.