FILE - In this Wednesday, Dec. 28, 2016, file photo, Afghan security personnel inspect the site of roadside bomb blast in Kabul, Afghanistan. The U.N. mission in Afghanistan says the number of civilian casualties in the country’s conflict rose by 3 percent in 2016. The U.N. 2016 Annual Report on the Protection of Civilians in Armed Conflict in Afghanistan was released Monday, Feb. 6, 2017. (AP Photo/Rahmat Gul, File)
FILE - In this Wednesday, Dec. 28, 2016, file photo, Afghan security personnel inspect the site of roadside bomb blast in Kabul, Afghanistan. The U.N. mission in Afghanistan says the number of civilian casualties in the country’s conflict rose by 3 percent in 2016. The U.N. 2016 Annual Report on the Protection of Civilians in Armed Conflict in Afghanistan was released Monday, Feb. 6, 2017. (AP Photo/Rahmat Gul, File) Credit: Rahmat Gul

KABUL, Afghanistan — More than 900 children were killed in Afghanistan’s conflict last year, the United Nations said Monday, calling it the most violent year for children since it started keeping records.

The U.N. mission said the nearly 25 percent increase in child deaths from the previous year was largely caused by mines and munitions left over from decades of conflict. It documented a 66 percent increase in such deaths in 2016.

“Conflict-related violence exacted a heavy toll on Afghanistan in 2016, with an overall deterioration in civilian protection and the highest-total civilian casualties recorded since 2009, when UNAMA began systematic documentation of civilian casualties,” the United Nations Assistance Mission in Afghanistan said in its annual report.

It said 3,498 people were killed in 2016, including 923 children, and that another 7,920 people were wounded. The overall casualty toll was slightly higher than the previous year.

“I am deeply saddened to report, for yet another year, another increase in civilian casualties, another all-time high figure,” Tadamichi Yamamoto, the U.N. envoy to Afghanistan, told a press conference.

The aid group Save the Children said the latest figures were “extremely concerning,” and called on all parties to do more to protect civilians.

The Taliban, who have been waging an insurgency against the U.S.-backed government in Kabul for more than 15 years, advanced on a number of fronts in 2016.