"The tally is modest by the standards of war historically, but every fatality is a tragedy and 11 years is too long," said Michael O'Hanlon, a fellow at the Brookings Institution in Washington. "All that is internalized, however, in an American public that has been watching this campaign for a long time. More newsworthy right now are the insider attacks and the sense of hopelessness they convey to many."
Attacks by Afghan soldiers or police - or insurgents disguised in their uniforms - have killed 52 American and other NATO troops this year.
"We have to get on top of this. It is a very serious threat to the campaign," the U.S. military's top officer, Army Gen. Martin Dempsey, said about the insider threat.
The top commander of U.S. and NATO forces in Afghanistan, Gen. John Allen, was blunter. "I'm mad as hell about them, to be honest with you," Allen told CBS's 60 Minutes in an interview broadcast on Sunday. "It reverberates everywhere across the United States. You know, we're willing to sacrifice a lot for this campaign, but we're not willing to be murdered for it."
The insider attacks are considered one of the most serious threats to the U.S. exit strategy from the country. In its latest incarnation, that strategy has focused on training Afghan forces to take over security nationwide - allowing most foreign troops to go home by the end of 2014.
As part of that drawdown, the first 33,000 U.S. troops withdrew by the end of September, leaving 68,000 still in Afghanistan. A decision on how many U.S. troops will remain next year will be taken after the American presidential elections. NATO currently has 108,000 troops in Afghanistan - including U.S. forces - down from nearly 150,000 at its peak last year.
The program to train and equip 350,000 Afghan policemen and soldiers has cost U.S. taxpayers more than $22 billion in the last three years.
The most recent attack came just days after Defense Secretary Leon Panetta said most U.S. and coalition combat units in Afghanistan returned to their practice of partnering with Afghan forces, nearly two weeks after the top U.S. commander put restrictions on such cooperation.
Like so many other deaths in Afghanistan, the latest were shrouded in confusion and conflicting accounts.
On Sunday, U.S. officials confirmed the deaths of two Americans, a service member and a civilian contractor killed late Saturday.
The fighting started when insurgents attacked a checkpoint set up by U.S. forces in eastern Wardak province, said Shahidullah Shahid, a provincial government spokesman. He said the insurgents apparently used mortars in the attack. The Americans thought they were under attack from their allies at a nearby Afghan army checkpoint and fired on it. The Afghan soldiers returned fire, Shahid said.
The Afghan Defense Ministry spokesman said the shooting broke out as a result of a "misunderstanding" while ISAF forces were on patrol near an Afghan army checkpoint.
NATO's International Security Assistance Force, commonly referred to as ISAF, gave a different account of the fighting in Sayd Abad district.
"After a short conversation took place between [Afghan army] and ISAF personnel, firing occurred which resulted in the fatal wounding of an ISAF soldier and the death of his civilian colleague," the coalition said in a statement. It said the three Afghan soldiers died "in an ensuing exchange of fire." NATO did not say whether it considered this an "insider" attack.
In Washington, Pentagon press secretary George Little said 2,000 deaths is one of the "arbitrary milestones defined by others " that the administration does not mark. "We honor all courageous Americans who have paid the ultimate sacrifice in Afghanistan to make the American people more secure," he said.
In addition to the 2,000 Americans killed since the Afghan war began on Oct. 7, 2001, at least 1,190 coalition troops from other countries have died, according to iCasualties.org, an independent organization that tracks the deaths.
Tracking deaths of Afghan civilians is much more difficult. According to the U.N., 13,431 civilians were killed in the Afghan conflict between 2007, when the U.N. began keeping statistics, and the end of August.