The car bomb is the second in less than two months in Aden [Reuters]

A car bomb targeting a military facility has killed at least four people and wounded 21 in Aden, the main city in southern Yemen, officials at the Yemeni defence ministry said.

The blast occurred as troops prepared to leave the facility for Abyan province, where security forces are engaged in fierce fighting with groups suspected of ties to al-Qaeda, soldiers reported to the AFP news agency on Sunday.

Medics and soldiers at the scene of the blast contradicted the death toll stated by the ministry and said that at least eight people had died, among them two senior officers, a major and a lieutenant-colonel.

"We were preparing to leave for Abyan when a car came in front of the gate of the camp, and then there was a huge explosion," one soldier said.

The defence ministry said the attacker, who also died in the explosion, hit a convoy at the checkpoint that had been headed to reinforce a military offensive on Abyan's provincial capital of Zinjibar, which the army has been trying to recapture for over a week.

Al-Qaeda blamed

The blast comes days after a car rigged with explosives blew up and killed a British ship surveyor in Aden, which officials say was a targeted attack against the long-time resident.

The car bomb was the second in less than two months in Aden and followed repeated warnings by officials that al-Qaeda-linked fighters were infiltrating the Arabian Sea port city to prepare for attacks there against security forces.

Hakim al-Masmari, the editor of the Yemen Post, said a security official had told him that al-Qaeda was responsible. "Security had not been increased in Aden since recent attacks,"  Masmari said.

Thousands of people have been displaced by fighting in Zinjibar between security forces and the fighters.

Ayad al-Shabwani, a leader of the Yemen-based Al-Qaeda in the Arabian Peninsula (AQAP) was killed during fighting near Zinjibar on Tuesday, a military official said.

Islamist groups control two cities in neighbouring Abyan province and have held on to them in the face of numerous air strikes and a ground offensive by government forces.

Yemen is home to one of the most active al-Qaeda branches in the world.

Additionally, the country has been in turmoil for nearly six months, with near daily massive street protests demanding longtime leader Ali Abdullah Saleh should step down.

The unrest has created a power vacuum and has allowed AQAP to capture and hold territory in parts of the nearly lawless south of the country, causing alarm in the US and in Yemen's rich Gulf Arab neighbours.

Source: Al Jazeera and agencies