More than 40 insurgents were killed Saturday as hundreds of coalition troops, many dropped by helicopter, wrested a town from the Taliban and U.S. forces battled militants across the south, officials said.

The U.S. military, meanwhile, agreed to help an Afghan government probe into reports that a coalition air raid killed civilians Monday in southern Uruzgan province. The military said it killed 40 extremists, but wounded residents said at least four civilians died.

President Hamid Karzai, who has repeatedly deplored coalition military operations that kill Afghans, ordered a second inquiry into Saturday's air assault in the southern Helmand insurgent stronghold of Sangin, as well as Wednesday's fighting in nearby Nawzad. At least 29 insurgents died in both.

Widespread violence across southern Afghanistan has killed about 800 people, mostly militants, since May, according to an Associated Press tally of coalition and Afghan figures.

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The bloodshed marks the deadliest period since U.S.-led forces toppled the Taliban regime in late 2001.

More than 300 British paratroopers, backed by hundreds more U.S. and Canadian forces, launched an early morning raid in Sangin, where "hundreds" of Taliban had massed in preparation for attacks, said coalition spokesman Maj. Scott Lundy.

"The coalition conducted a large-scale air assault before dawn, with helicopter-borne infantry dropped on several positions," Lundy said. "Coalition forces killed 10 Taliban and drove the others out, but it is difficult to say if the remainder are still nearby."

The assault was part of Operation Mountain Thrust, an anti-Taliban offensive involving more than 10,000 U.S.-led troops.

Coalition forces will remain in Sangin until the Taliban threat has been wiped out and Afghan authorities can reach out to impoverished residents to promote reconstruction efforts, Lundy said.

Afghan forces killed another eight militants in Sangin on Thursday, the country's Defense Ministry said.

The Sangin Valley is a "natural corridor" for Taliban and criminal movement in southern Afghanistan, plus opium poppy cultivation, some of the proceeds of which are believed to be used by the Taliban to buy weapons, Lundy said.

U.S.-led troops and Afghan soldiers also killed an estimated 31 insurgents in several firefights in Uruzgan province's Chora district, said Lt. Col. Paul Fitzpatrick.

American forces have pledged to provide all available information to an Afghan government investigation into Monday's air raid on Uruzgan's provincial capital of Tirin Kot.

Close air support was used to target "extremists" firing from buildings in Tirin Kot at coalition forces, a military statement said.

Karzai ordered a second investigative team report on Saturday's clashes in Sangin and Wednesday's air strikes in Nawzad, said Assan Tahiri, a presidential palace official.

Tahiri said that there were civilian casualties and property damage in both areas, and that the Afghan government will compensate victims. He did not elaborate.

The U.S. military said there was no indication that any civilians were killed in Nawzad. One of six air raids destroyed an unused school building from which insurgents were allegedly firing mortars.

The Afghan Human Rights Commission condemned the continued coalition-insurgent violence in the south.

"The fighting, bombing and military operations impact on the civilian community and are unacceptable for us," the commission said in a statement.

In other violence, Afghan and coalition soldiers killed two male "foreigners" wearing burqas — the body-shrouding veil worn by many Afghan women — and detained five Taliban in Uruzgan's Dihrawud district Friday, the Defense Ministry said. The foreigners' nationalities were not released. Soldiers confiscated an explosives-rigged vest and 16 roadside bombs.

Afghan and coalition soldiers battled 20 insurgents in Uruzgan, killing one, the U.S. military said.

In Zabul, Afghan soldiers killed four militants Friday after they attacked their convoy, while a Taliban rocket-propelled grenade attack on a coalition supply convoy killed one bystander and wounded a truck driver, Afghan officials said.