Taliban commanders sometimes deliberately target non-U.S. contingents because they know that in many countries, public opposition to the war tracks any sudden rise in the number of battlefield deaths.
Another relatively low-tech weapon, the rocket-propelled grenade, caused the worst single U.S. troop loss of the war. Thirty Americans and eight Afghans were killed in the Aug. 6 crash of a Chinook helicopter carrying mainly elite Navy SEALs.
"In 2011 we fought more strongly than in any year before, and staged more high-profile attacks than in previous years," said Mujahid, the Taliban spokesman. Chief among those assaults, he said, were September's 20-hour siege of the U.S. Embassy in Kabul and a similar prolonged attack on the landmark Intercontinental Hotel in the capital three months earlier.
The Taliban's continuing shift away from conventional battlefield confrontations led to growing numbers of civilian deaths in the first three-quarters of last year, according to the United Nations.
There was some indication such deaths might be turning the Afghan public against the Taliban; an Asia Foundation study released in November found decreasing support among Afghans for the movement's goals. But concern over civilian casualties cuts both ways.
Throughout the year, Karzai voiced harsh criticism of U.S.-led operations that he said posed undue hazards to Afghan citizens.
The Afghan leader's demand for an end to American participation in nighttime raids on residential compounds emerged as a potentially serious obstacle to a long-term partnership agreement, which will govern the U.S. military presence after 2014.
As 2012 begins, the Afghan government and the Obama administration are looking for ways to negotiate a settlement with the Taliban.
In late December, Karzai agreed to the opening of a Taliban liaison office in Qatar, though some members of his administration fear U.S. officials will keep them in the dark about their contacts with the insurgents.
Pakistan's role will be crucial too, but the prospects for help seemed dim because of a sharp deterioration in ties between Washington and the government in Islamabad.
The Taliban leadership ended the year on a taunting note, asserting that the Americans were looking for a way out, just like the Soviet invaders who arrived 32 years ago. "They are on the point of fleeing," it said in a statement.
U.S. and NATO officials stressed that they were not abandoning the country, but preparing for an orderly transfer.
"At the end of 2011, we have three years to go, and that is more than enough to finish the job," said German Brig. Gen. Carsten Jacobson, a spokesman for the NATO force. "We are not leaving because we have to. We are leaving because we can."