The commander of military forces in the south of Yemen was killed by a suicide bomber in the port city of Aden on Monday, days after troops drove Islamist militants linked to al Qaeda from their southern strongholds.

The killing of Major General Salem Ali Qatan highlighted the tenuous grip of Yemen's central authorities on the south despite a month of US-supported bombardments and airstrikes aimed at crushing the militants.

The Defence Ministry said a suicide bomber hurled himself at Qatan's vehicle, also killing two soldiers escorting him. It identified the bomber as a Somali but gave no other details. Pools of blood coated the street where the bomber struck.

A doctor at the hospital where Qatan died said 12 other people, nine of them soldiers, were wounded in the attack in Aden, a port city overlooking oil shipping lanes fewer than 100 km from several cities which Islamists flying Al Qaeda's banner recently controlled.

Most of that territory is in Abyan province, where fighters calling themselves Ansar al-Sharia seized towns last year, taking advantage of protests against the three-decade rule of then leader Ali Abdullah Saleh.

Saleh, who gave way to his deputy in February under a US and Saudi-brokered power transfer, had redeployed some of his forces from the south in a bid to put down protests, ultimately killing hundreds of demonstrators.

Abyan has been the focus of a month-old offensive Yemen's army mounted with support from the US, which wages its own campaign of drone and missile strikes against alleged al Qaeda members.

Washington is increasingly concerned about the militant presence in Yemen and has backed the military with training, intelligence, and increased aid although the Pentagon has declined to give details of the scale of the assistance.

The Yemeni military last week said it had driven Islamist fighters from territory they had held for over a year, including Zinjibar, capital of Abyan province, and another city, Jaar.

It is now attacking Islamists in another southern province, Shabwa, to where fighters who quit towns in Abyan have fled.

Provincial officials said two soldiers were killed in an ambush on Monday in Ataq, by fighters trying to reach the town of Azzan, where Islamists retain a presence.

Qatan was a central figure in plans to restructure Yemen's military, which split into warring factions during the struggle of over Saleh's fate. His appointment to the southern command was the first move by President Abd-Rabbu Mansour Hadi against the former president's loyalists in the army.

An official in Hadi's office called Qatan's killing 'a great loss for Yemen and the war on terrorism.'-Reuters