The brother-in-law of fugitive Taliban leader Mullah Mohammad Omar is one of the key figures under siege in a mountain hideout, the Afghan defence ministry said. The claim could not be independently confirmed.

"One-hundred-and-thirty-two Taliban were killed," in the operation in a restive area on the borders of Kandahar, Zabul and Uruzgan provinces, defence ministry spokesman Mohammed Nu'man Atifie told AFP.

"If you look at the number of the men they've lost we can say that their backbone is broken," Atifie added. "It has been a great, great success for the government."

Thirty-two rebels were killed when the offensive began early Tuesday and a further 100 insurgents were killed later Tuesday and in the early hours of Wednesday morning in Mian Nisheen district, the spokesman said.

Most of the militant deaths occurred when US warplanes armed with laser-guided bombs and supported by British aircraft pounded suspected Taliban safe havens, US and Afghan officials said.

Around 200 Afghan police and many more Afghan and US-led coalition troops were hunting down surviving pockets of rebels hiding out in valleys in the "black triangle" -- named after the Taliban's distinctive black turbans.

Four Taliban commanders including Mullah Brader, who is related by marriage to the one-eyed Mullah Omar and is also said to be the militia's current deputy, have been ringed by government forces north of Mian Nisheen, Atifie said.

Afghan officials described the onslaught as an attempt to curb a strong resurgence by the fundamentalist Islamic militia before important parliamentary elections in less than three months' time.

Three Afghan policemen were also killed in the operation, Kandahar province police chief Mohammed Ayoob Salangi told AFP. The US military has said that five American soldiers were wounded.

"The Afghan national police are the lead on this. We are supporting what they are doing," said US military spokeswoman Lieutenant Cindy Moore.

A US Air Force U-2 spy plane returning from a mission over Afghanistan crashed during landing late Tuesday at an air base in the United Arab Emirates, according to reports in the Arab sheikhdom and the US military.

The US military would not reveal if the mission was linked to the operation in Afghanistan.

British military spokeswoman Lieutenant Gemma Fullman said British planes equipped with air-to-surface missiles provided close air support during the operation in southern Afghanistan but did not drop any munitions.

The Taliban's usual spokesman was not immediately available to comment.

Many of the rebels targeted by the offensive are thought to have taken part in a daring raid last week on Mian Nisheen in which the rebels took 31 people hostage.