KABUL, Afghanistan -- The number of U.S. drone strikes in Afghanistan rose sharply last year compared with 2011, the United Nations said Tuesday. The increase was a sign that unmanned aircraft are taking a greater role as the U.S. military tries to streamline the fight against insurgents while preparing to withdraw combat forces in less than two years.
Drones have become a major source of contention between the United States and countries such as Pakistan, where covert strikes on militant leaders have drawn condemnation and allegations of sovereignty infringements as family members and other bystanders are killed.
They have not been a prominent issue in Afghanistan, however. While drone attacks have occurred, they have largely been in support of ground troops during operations and have not been singled out by President Hamid Karzai's administration in its campaign against international airstrikes.
The steep rise in the number of weapons fired from unmanned aerial aircraft -- the formal term for drones -- raises the possibility that it may become more of an issue as U.S. forces grow more dependent on such attacks to fight al-Qaida and other insurgents after combat troops exit by the end of 2014.
The U.N. mission in Afghanistan, or UNAMA, said 506 weapons were released by drones in 2012, compared with 294 the previous year. Five incidents resulted in casualties, with 16 civilians killed and three wounded -- up from just one incident in 2011.
Georgette Gagnon, UNAMA's head of human rights, said it was the first year the United Nations had tried to document civilian casualties from drones. The U.S. Air Force Central Command also recorded an increase, giving the numbers of weapons released by drones as 243 in 2009, 277 in 2010, 294 in 2011 and 494 in 2012.
Drones are highly effective, and most nations have given Washington at least tacit agreement to carry out the attacks.
Peter Singer of the Washington-based Brookings Institution noted that the drone program in Afghanistan is run by the Pentagon, and therefore is more transparent than the CIA drone counterterrorism program in Pakistan. Mr. Singer, who has written extensively about drones, said the number of operations in Afghanistan is increasing, but most are performed in support of troops on the ground. "This is just another sign of how drones are becoming the new normal," he said.
The U.N. figures were released as part of its annual report on civilian casualties in Afghanistan. Overall, the full-year toll of civilian deaths in 2012 declined to 2,754, a 12 percent decrease from 3,131 in the same period a year earlier. It was the first time in six years that the civilian death toll dropped.
But the toll spiked in the second half of the year when weather improved, compared with the same period in 2011, suggesting that Afghanistan is likely to face continued violence as the Taliban and other militants fight for control following the impending withdrawal by U.S. and allied combat forces.
The population also faced a sharp increase in assassinations and other insurgent attacks targeting government supporters.
Conflict-related violence struck more women and girls last year as well, with 301 killed and 563 wounded -- a 20 percent increase from 2011, the report said.
The findings come as the war is reaching a turning point, with international troops increasingly taking a back seat in operations, and Afghan government forces leading.
The total number of civilian deaths by airstrikes fell for the year after the U.S.-led coalition implemented stricter measures to prevent innocent people from being killed.
The United Nations said most civilian casualties from drone strikes appeared to be the result of weapons aimed directly at insurgents, but some may have been targeting errors. It cited the example of four boys killed in Logar province Oct. 20, when a drone struck after a clash between pro-government forces and insurgents a few miles away.
UNAMA called for a review of tactical and operational policy on targeting to ensure compliance with international humanitarian law "with the expansion of the use of unmanned combat aerial vehicles" in Afghanistan.
Pentagon spokesman George Little said the U.S. military works hard to protect civilians. "We take great care with our unmanned systems to conduct very precise targeting in Afghanistan, and we will continue to do so. When there are mishaps, we take steps to work closely with the government of Afghanistan and the affected individuals to express our concerns," he said in Washington.
UNAMA said civilian casualties rose 13 percent, to 4,431, in the year's second half, including more from roadside bombs in public areas, compared with the same period in 2011. It cited a growing number of civilian casualties from roadside bombs, even as fewer bystanders were hurt in ground engagements in the country's troubled south and east.
An Afghan Interior Ministry spokesman pledged to do everything possible to stop the insurgents from attacking civilians. "They're still using suicide bombers, they still use IEDs [roadside bombs] in the very populated areas, and they still use civilians as a shield in the villages," Interior Ministry spokesman Sediq Sediqi said. "The important thing is that civilian casualties should be decreased to zero."