Civilian deaths caused by the war in Afghanistan have dropped for the first time in six years, the United Nations said Tuesday in its annual report on the conflict’s toll on noncombatants.

The report linked the 12 percent drop in civilian deaths in 2012 to reduced ground fighting by the warring sides, chiefly the Taliban and U.S. troops; a decrease in the number of NATO coalition airstrikes; and fewer suicide attacks by insurgents.

However, U.N. officials noted increasing threats to noncombatants last year because of the reemergence of armed groups, including pro-government militias, especially in the country’s north and northeast. Those regions generally have been regarded as secure compared with the south and the east, where Taliban-led militants are most active.

The United Nations recorded 2,754 civilian deaths in Afghanistan in 2012, compared with 3,131 in 2011. Since 2007, when the world body began keeping these statistics, 14,728 civilians have been killed in the conflict.

For years, civilian deaths caused by foreign troops have been a thorny issue between President Hamid Karzai and his Western backers, especially the United States, even though, according to the U.N. report, militants are responsible for far more such casualties — 81 percent in 2012 — than NATO forces. Eight percent of civilian casualties were attributed to coalition forces, the report said; 11 percent percent were not linked to a specific cause.

Civilian casualties resulting from air operations by Western forces dropped by 42 percent in 2012 compared with 2011, the report said, data that support NATO’s oft-stated position that its airstrikes against militants have become more precise.

But the report stressed “the still critical need for continuous review of targeting criteria” to further reduce civilian deaths from aerial attacks. “Of the 126 civilian deaths from aerial operations, 51 were children,” the report noted.

To illustrate the inherent risk of aerial attacks, the United Nations singled out a Sept. 16 series of strikes that killed eight people in Laghman province, mainly women and children, but no militants.

“The decrease in civilian casualties . . . is very much welcome,” said Jan Kubis, the U.N. special envoy for Afghanistan. “Yet, the human cost of the conflict remains unacceptable.”

The use of roadside bombs by insurgents was the “single biggest killer of civilians,” Kubis said.

After 10 civilians died last week in a NATO airstrike that was requested by Afghan security forces in eastern Konar province, Karzai issued a decree that bars the national forces from seeking such air support in residential areas.

On Sunday, Gen. Joseph F. Dunford Jr., the top U.S. and NATO commander in Afghanistan, expressed support for Karzai’s order and said the international coalition can operate effectively despite the ban.