The announcement came as four Italian troops were killed and one seriously wounded in an insurgent roadside bomb attack Saturday in the country's west.
Violence continues unabated throughout much of Afghanistan. The focus of the U.S.-led war, which entered its 10th year last week, has been on the south, but coalition troops are increasingly fighting resilient militants in both the east and north.
The aid worker, identified as Linda Norgrove, was killed Friday night by her captors during the operation to free her, Foreign Secretary William Hague said in a statement from London.
Ms. Norgrove and three Afghan colleagues were kidnapped in eastern Kunar province on Sept. 26 after being ambushed. Police fought a gunbattle with the kidnappers near the attack site before the assailants fled. Ms. Norgrove's co-workers were released shortly afterward.
“It is with deep sadness that I must confirm that Linda Norgrove … was killed at the hands of her captors in the course of a rescue attempt last night,” Mr. Hague said.
“Working with our allies we received information about where Linda was being held and we decided that, given the danger she was facing, her best chance of safe release was to act on that information,” Ms. Hague said.
Details about the failed raid were sketchy. Both British and NATO officials refused to provide more specific information, each side referring questions to the other.
“Afghan and coalition security forces did everything in their power to rescue Linda,” said Gen. David Petraeus, the top commander of U.S. and NATO forces in Afghanistan. “Linda was a courageous person with a passion to improve the lives of Afghan people, and sadly she lost her life in their service.”
Ms. Norgrove worked for Development Alternatives Inc., a global consulting company based in the Washington, D.C., area. DAI does contract work in Afghanistan for the United States Agency for International Development, or USAID.
“We are saddened beyond words by the death of a wonderful woman whose sole purpose in Afghanistan was to do good — to help the Afghan people achieve a measure of prosperity and stability in their everyday lives as they set about rebuilding their country,” DAI President and CEO James Boomgard said.
The four Italian soldiers were killed and another was wounded seriously in a bomb blast Saturday in western Farah province, said Gen. Massimo Fogari, a spokesman for Italy's Defence Ministry.
The bomb exploded as a 70-vehicle convoy passed by insurgents, and then the soldiers came under small-arms fire.
Prime Minister Silvio Berlusconi said he was saddened “by the tragic ambush.”
“We are grateful to all Italian soldiers who, in various missions around the world, allow our country to keep its international commitments in support of peace and against any form of terrorism,” Berlusconi said in a statement.
The deaths brought to 24 the number of NATO forces killed this month. At least 2,012 NATO service members have died since the U.S.-led invasion of Afghanistan on Oct. 7, 2001, according to an Associated Press count.
Friday's attempted rescue operation wasn't the first of an abducted Briton in Afghanistan to end in bloodshed. New York Times reporter Stephen Farrell and translator and reporter Sultan Munadi were taken hostage in September 2009 when they went to cover a NATO airstrike that killed scores of civilians in northern Afghanistan.
Mr. Munadi and a British commando died in the raid that rescued Mr. Farrell.
In August, unidentified gunmen killed 10 members of a charity medical team, including Briton Dr. Karen Woo, six Americans, a German and two Afghans. The aid workers for the International Assistance Mission were shot and killed by militants in Badakhshan province, which neighbours Kunar to the north, as they returned from providing health care in remote villages.
Northern Afghanistan has been the scene of escalating violence amid intensified military operations by NATO and Afghan forces.
Saturday's events came a day after a powerful blast at a mosque packed with worshippers killed at least 20 people — including a provincial governor — in Taluqan, capital of northern Takhar province. Thirty-five others were wounded in the brazen attack.
A suspected suicide bomber targeted and killed Mohammad Omar, governor of neighbouring Kunduz province. The assassination came just days after he publicly warned of escalating threats from Taliban and foreign fighters across the north.
No group claimed responsibility, but the Taliban have targeted Omar previously.
Meanwhile, President Hamid Karzai flew to volatile southern Afghanistan to meet with more than 200 tribal elders and seek their support for his government's effort to extend its influence beyond Kabul.
Mr. Karzai was accompanied by Gen. Petraeus, U.S. Ambassador Karl Eikenberry, and top Afghan security officials on the trip to troubled Kandahar province.
Kandahar is the scene of NATO's Operation Dragon Strike, targeting the Taliban in their southern strongholds. The operation aims to rout insurgents from areas they have long controlled.
In other violence, NATO and Afghan forces killed two senior Taliban leaders and two other fighters after raiding a compound in eastern Afghanistan, the military alliance said Saturday.
Mullah Hezbollah, who operated in Wardak province, died in a gunbattle during an operation Thursday night, NATO said. Another Taliban leader, Qari Sulayman, was also killed along with the two other insurgents in the raid.
NATO also announced Saturday that joint forces seized more than 6,600 pounds (3,000 kilograms) of drugs — including heroin and opium — a day earlier from vehicles searched in southern Afghanistan.