It was the heaviest U.S. loss of life in a single battle since July 2008, when nine American soldiers were killed in a raid on an outpost in Wanat in the same province.
Gen. Stanley McChrystal, the top U.S. and NATO commander in Afghanistan, plans to shift U.S. troops away from remote outposts that are difficult to defend and move them into more heavily populated areas as part of his new strategy to focus on protecting Afghan civilians.
U.S. troops used artillery, helicopter gunships and airstrikes Saturday to repel the attackers, inflicting "heavy enemy casualties," according to a NATO statement. Fighting persisted in the area Sunday, U.S. and Afghan officials said.
The Taliban claimed responsibility for the attack. NATO spokesman Brig. Gen. Eric Tremblay said the assailants included a mix of "tribal militias," Taliban and fighters loyal to Sirajudin Haqqani, an al-Qaida-linked militant based in sanctuaries in the tribal areas of Pakistan near the Afghan border.
Afghan authorities said the hostile force included fighters who had been driven out of the Swat Valley of neighboring Pakistan after a Pakistani military offensive there last spring.
"This was a complex attack in a difficult area," U.S. Col. Randy George, the area commander, said in a statement. "Both the U.S. and Afghan soldiers fought bravely together."
Details of the attack remained unclear Sunday and there were conflicting reports of Afghan losses due to poor communications in the area, located just 20 miles (30 kilometers) from the Pakistani border and about 150 miles (230 kilometers) from Kabul.
A NATO statement said the attacks were launched from a mosque and a nearby village on opposite sides of a hill, which included the two outposts - one mostly American position on the summit and another mostly Afghan police garrison on a lower slope.
NATO said eight Americans and two Afghan security troopers were killed.
An Afghan military official, speaking on condition of anonymity because of security issues, said three Afghan soldiers and one policeman had been killed in two days of fighting. He also said at least seven Afghan army soldiers were missing and feared captured.
In addition, provincial police chief Mohammad Qasim Jangulbagh said 15 Afghan policemen had been captured, including the local police chief and his deputy. Jangulbagh estimated that about 300 militants took part in the attack.
"Kamdesh is one of the most dangerous areas of Nuristan province," he said, noting that the area is across the border from parts of Pakistan where al-Qaida-linked militants operate.
Jangulbagh said that after Pakistani forces drove militants from most of the Swat Valley five months ago, militants "received orders to come to Nuristan and destabilize the situation."
Taliban spokesman Zabiullah Mujahid said militants overran both outposts, but U.S. spokeswoman Capt. Elizabeth Mathias said U.S. troops were holding the outposts Sunday. She also said a roadside bomb killed a U.S. service member southwest of Kabul on Saturday, bringing the U.S. death toll for the month to 15.
The fighting occurred in a region where towering mountains and dense pine forests have long served as a staging area for Taliban and al-Qaida fighters who move freely across the Pakistani frontier.
The region was a key staging area for Arab militants who fought alongside Afghan warriors during the U.S.-backed war against the Soviets in the 1980s and is one of the few parts of South Asia where Muslims follow the hardline Wahhabi sect of Islam.
The weekend fighting was reminiscent of the July 2008 battle of Wanat when an estimated 200 militants stormed an outpost defended by about 70 U.S. and Afghan soldiers, nearly overrunning the position.
Last week, Army Gen. David Petraeus ordered a new investigation into the Wanat fighting due to allegations of mismanagement by senior commanders.
The Wanat fighting convinced U.S. commanders that they should move Western forces away from remote areas where foreigners are unwelcome to more populated parts of the country, closing outposts such as the ones attacked Saturday.
However, the governor of Nuristan, Jamaludin Badar, complained that more - not fewer - Western troops should be sent to the area to stop infiltration from Pakistan.
"We had concerns about security in Kamdesh and we have already asked for extra forces," he told The Associated Press. "If there are fewer security forces, this sort of thing will happen again."
He also complained about a lack of coordination between international forces and Afghans.