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KABUL, Afghanistan - U.S. and U.K. military officials have started what's promised as a thorough investigation into the death of a kidnapped British aid worker who may have been killed in error by U.S. special forces -- rather than, as originally stated, by her Taliban captors.

Linda Norgrove's death has reverberated through the corridors of power from Kabul, to London, to Washington -- where President Barack Obama expressed condolences and pledged "to get to the bottom" of what happened during the deadly raid.

Norgrove, 36, and six insurgents were killed Friday night after U.S. special forces stormed a compound in eastern Kunar province where she had been held for two weeks. Norgrove and three Afghan colleagues were ambushed and kidnapped Sept. 26. Her colleagues were quickly freed.

NATO said initially Norgrove was killed by her captors. On Monday, however, alliance officials said new information indicated Norgrove may have been killed by a U.S. grenade.

"The review showed what was believed to be a member of the rescue team throwing a hand grenade in the area near where Ms. Norgrove was later found," said NATO spokeswoman Maj. Sunset Belinsky. "It's now unclear what the exact circumstances surrounding her death are, and the investigation will attempt to determine the facts."

The White House said Obama and British Prime Minister David Cameron both said the rescue operation was necessary and "agreed that it was now essential to get to the bottom of what had happened."

NATO Secretary-General Anders Fogh Rasmussen emphasized that "whatever happened, I would like to stress that those who are responsible of course are the captors."

British Foreign Secretary William Hague told parliament Monday Norgrove's kidnappers were members of a local Salafist group allied to the Taliban, al-Qaida, and other insurgents. Salafist militants seek to revive strict Muslim doctrine dating to the 6th century Prophet Muhammad.

"At no stage was any serious attempt made to negotiate by those holding her," Hague said.

The probe will be led by U.S. Army Maj. Gen. Joseph L. Votel of U.S. Special Operations Command. The U.K. will appoint Brig. Rob Nitsch, head of logistics for British forces in Afghanistan, to "work closely" with the Votel, Britain's prime minister's office said.

All British citizens who die abroad are entitled to a formal inquest into their death. NATO officials say they hope the investigation will be completed quickly.

Meanwhile, an Afghan interpreter was killed and seven NATO troops and an Afghan police officer were wounded when insurgents fired a rocket-propelled grenade into their helicopter in Kunar Tuesday, the alliance said.

The CH-47 Chinook helicopter -- with 26 people aboard -- had just landed and was off-loading when the RPG was launched into its cargo bay.

Also, a NATO service member died in a highway bombing in the south, and 11 civilians were killed in an insurgent rocket attack and roadside blasts in the east, Afghan officials and NATO said Tuesday.

NATO did not give a nationality or exact location of the service member's death Tuesday, which brought 28 the number of troops killed in October. At least 2,016 NATO service members have died since the U.S.-led invasion of Afghanistan on Oct. 7, 2001, according to an Associated Press count.

Violence has risen particularly sharply in the south in recent months, along with a surge of U.S. forces targeting Taliban strongholds.

That has led to record numbers of patients with war wounds seeking treatment at the main hospital in southern Kandahar city, the Red Cross said Tuesday.

About 1,000 patients came to Mirwais Regional Hospital with weapon-related injuries in August and September, about twice number from the same period of 2009, said the Red Cross aid.

The sharp jump this year was likely caused by the increasing number of armed groups operating in the area, said Reto Stocker, chief of the International Committee for the Red Cross in Kabul.

"Our greatest challenge consists in maintaining access to the areas hardest hit by the fighting, but the multiplication of armed groups is making this much harder for us," Stocker said.

Attacks in the east included an insurgent rocket, which hit a vehicle carrying civilians in Jani Khel district of eastern Paktika province. Six people died, the Interior Ministry said.

Mohammad Jan Rasoulyar, spokesman for the governor of southeastern Zabul province, said another group of civilians riding in a vehicle hit a roadside bomb Monday night in Shahjoy district. Four were killed. The same day, an Afghan civilian died in a roadside bombing in the Ismail Khel district of eastern Khost province.

Afghan civilians are killed by roadside bombs and other violence almost daily. A U.N. report said more than 1,200 civilians died and nearly 2,000 were wounded between January and June this year.