Yemeni troops launched an all-out offensive on Saturday to retake the southern city of Zinjibar, held for a year by Al-Qaeda gunmen, in fighting that killed 12 people, military and local sources said.

And in eastern Yemen, a US drone struck a vehicle transporting Al-Qaeda militants, killing six gunmen who were on board, as air raids against the jihadist network intensified, a local official said

The "wide offensive" began from three sides and was supported by the air force and the navy, said a military official, adding that Defence Minister Mohammed Nasser Ahmed was supervising the operation from nearby.

"The defence minister is supervising a military plan to regain control of the city of Zinjibar and (the neighbouring town of) Jaar from Al-Qaeda gunmen," the official said.

Two soldiers, including a colonel, were killed in the fighting, while 12 others were wounded, he said.

Six fighters of the Al-Qaeda-linked Partisans of Sharia (Islamic law), were also killed in the attack, said a tribal source in Jaar, to where the gunmen evacuate their casualties.

The militants took control of Zinjibar, the provincial capital of Abyan, in May last year. They also control Jaar and other parts of the province.

Military units also attacked Jaar from the west, the military official said, adding troops reached the area of Kadama, on the outskirts of the town.

In the morning, air strikes hit Jaar, killing three Al-Qaeda gunmen and a civilian, and wounding three civilians, a tribal source said.

The air raids were to pave the way for advancing troops, said another military official.

Meanwhile, a local official in Shabwa said a US drone killed six militants when it targeted a vehicle carrying them on the road linking Shabwa with Marib, east of Sanaa.

"A US drone targeted a vehicle of Al-Qaeda between Shabwa and Marib. It killed six members of the organisation," he said, adding they were traveling from Marib to Shabwa.

Attacks on Al-Qaeda by Yemeni forces and suspected US drones have increased lately, including an air raid in eastern Yemen on Sunday that killed jihadist network leader Fahd al-Quso, who was wanted in connection with the 2000 bombing of the USS Cole.

Quso's name figured on an FBI list of most wanted terrorists, along with a reward of up to $5 million for information leading to his arrest.

US media reported that a Saudi spy, reportedly a "mole" or "double agent," spent weeks with Al-Qaeda in the Arabian Peninsula (AQAP) and garnered sensitive information that allowed the CIA to launch the drone strike against Quso.

The reports said the "mole" had been ordered by AQAP to blow up a US-bound airliner.

A senior US official told the New York Times the bomb for the attack was sewn into "custom fit" underwear that would have been difficult to detect even in a pat-down at an airport.

Yemen's new president, Abdrabuh Mansur Hadi, vowed last week to intensify the war against Al-Qaeda, which has made much of the lawless southern and eastern part of the country a safe haven.