NATO will investigate whether a grenade thrown by American military forces killed a British aid worker during a botched rescue in Afghanistan last week, an alliance spokesman said Monday.

Linda Norgrove, 36, was killed Friday in the raid by U.S. forces in Afghanistan's eastern Kunar province, after she and three colleagues were kidnapped two weeks earlier. NATO initially said Norgrove died when captors detonated a bomb as NATO forces attempted to free her.

However, British Prime Minister David Cameron said Monday that Norgrove was possibly killed by a grenade lobbed by a member of the U.S. special forces rescue team.

Cameron said he had informed Norgrove's family of the "deeply distressing development," and defended the decision to attempt the risky rescue mission.

"We were clear that Linda's life was in grave danger and the operation offered the best chance of saving her life," Cameron told reporters in London.

Lt. Col. John Dorrian, a spokesman at NATO headquarters in the Afghan capital Kabul, said Monday the rescue mission leader saw video footage of the raid, talked with members of the rescue team, and decided "it was not conclusive what the cause of her death was."

The rescue mission leader spoke with U.S. and NATO commander in Afghanistan, Gen. David Petraeus, who requested the investigation, Dorrian said. The probe will be led by U.S. Central Command.

Norgrove, who worked for U.S.-funded Development Alternatives Inc., was abducted in an ambush on Sept. 26 along with three Afghan colleagues who were later released. Six kidnappers also died in the rescue attempt.

NATO was also investigating Monday the deaths of two civilians in southern Afghanistan a day earlier. Initial reports indicated they were killed in a NATO airstrike called in after a patrol was attacked by insurgents.

In other violence, a roadside bomb killed a NATO service member in the south, the alliance said, without giving a nationality or exact location.

Monday's death brought to 27 the number of NATO forces killed this month. At least 2,015 NATO service members have died since the U.S.-led invasion of Afghanistan on Oct. 7, 2001, according to an Associated Press count.

In the east Monday, Taliban fighters ambushed a supply convoy guarded by Afghan military contractors as it traveled through Ghazni province on its way to Kandahar in the south, said provincial chief of police Zarawar Zahid. An hourlong gunbattle killed eight insurgents and wounded two Afghan security contractors in Qarabagh district.

Six militants died in operations by Afghan forces Sunday in southern Helmand province's Marjah and Greshk districts, the Defense Ministry said in a statement Monday.

A joint force was attacked with small-arms fire in southern Kandahar on Sunday, NATO said. Troops called in an airstrike and followed up by firing mortar rounds in Zhari district.

"Two civilians may have been accidentally killed," said NATO, adding a child was also wounded. One insurgent died, it said.

An Afghan civilian was also killed by a roadside bomb planted by insurgents in Khost province Monday, NATO said.

The nine-year war has inflicted a mounting toll on Afghan civilians. A U.N. report said more than 1,200 Afghans died and nearly 2,000 were wounded between January and June this year.

President Hamid Karzai confirmed his government has been in informal talks with the Taliban on securing peace in war-weary Afghanistan "for quite some time" _ the latest in a series of high-level acknowledgments of contacts with the insurgent group.

Unofficial discussions have been held with Taliban representatives over an extended period, Karzai told CNN's "Larry King Live" in an interview to be broadcast Monday.

The Afghan government says it hopes to make talks more structured with a "peace council" that will aim for formal talks with insurgent groups. On Sunday, former President Burhanuddin Rabbani was named chief of the council. Rabbani was one of a group of mujahedeen leaders who fought the Soviets in the 1980s. He was Afghanistan's president between 1992 and 1996, when he was ousted by the Taliban.

Omar said the panel should become the conduit for formal talks.

"We hope that the signals that have been sent from the different representatives of the Taliban, and the kind of contact, direct and indirect, from the past will materialize into substantive talks led by the High Council of Peace," Omar said.

Publicly, the Taliban have said they won't negotiate until foreign troops leave the country, yet many Taliban leaders have reached out directly or indirectly to the highest levels of the Afghan government, he said.

___

Associated Press writers Jill Lawless in London, and Deb Riechmann, Heidi Vogt and Amir Shah in Kabul contributed to this report.