The number of children killed and maimed in the Afghan war increased dramatically last year, according to the UN, which has documented the highest civilian casualty toll in the country since 2001.

In a report released on Monday, the UN documented 11,418 casualties, a 3% increase since 2015, including 3,498 deaths.

Child casualties rose 24% – to 923 killed and 2,589 wounded – mainly as a result of ground engagements closer to residential areas, and explosive remnants of war.

While the total number of killed marked a slight drop, the number of injured has grown 6% since 2016.

“It is about time the various parties to the conflict ceased the relentless commission of war crimes and thought about the harm they are doing to their mothers, fathers, children and future generations by continuing to fuel this senseless, never-ending conflict,” said Zeid Ra’ad al-Hussein, the UN high commissioner for human rights.

In early October in Kunduz, two helicopters defending the city against a Taliban assault fired rockets at a private house belonging to a shopkeeper, wounding four children. The oldest, who was 17, lost a leg.

“My poor son. His future will be very dark,” Hakim, the shopkeeper, told the Guardian. “This year, many more people were injured than last year.”

Aside from documenting the toll, the UN numbers reflect a changing war dynamic. Since 2014, international forces have largely withdrawn from the battlefield and fighting has moved into villages and closer to cities.

The leading cause of casualties is ground engagements. The UN attributes 61% of casualties to anti-government groups, chiefly the Taliban, and 22% to pro-government Afghan forces.

The Taliban controls or contests 97 of Afghanistan’s 407 districts, according to the Long War Journal. The militants are on the cusp of at least five provincial capitals, including in Helmand province where they now fire rockets into Lashkar Gah.

It was here, last week, that 14-year-old Qodratullah was shopping for bread for lunch when he was struck and killed by a rocket 20 metres from his house. A seventh-grade student, Qodratullah was one of two providers in the family. “We don’t have a father. We don’t have anyone to feed us,” his older brother, Ahmadullah, 17, said.

The battle for territory leaves another hazard in its wake: unexploded ammunition. The UN said 86% of casualties sustained by unexploded ordnance were children, with 183 killed and 426 injured, often when collecting scrap metal, tending to livestock or playing.

Last year, 15 years into the war and after nearly 100 countries had signed protocol V of the UN convention on certain conventional weapons, it was finally ratified by the Afghan government, obliging it to clear explosive remnants of war.

Villagers gather around the bodies of civilians killed in clashes between Taliban and Afghan security forces in Kunduz province. Photograph: Najim Rahim/AP

Improvised explosive devices, or IEDs, remain a severe danger. The UN documented a growing use of pressure-plate IEDs, which are indiscriminate and placed by militants leaving an occupied area but often end up harming returning, displaced families.

Small militant groups loyal to Islamic State (Isis) present a new type of danger to Afghan civilians. Three attacks in Kabul, including two on mosques, killed more than 100 people and targeted members of Afghanistan’s Shia minority, prompting the UN, for the first time in this type of report, to condemn possible “crimes against humanity”.

With the Taliban gaining ground and Isis digging in, the US upped airstrikes, from 947 in 2015 to 1,337 in 2016. As a result, the number of harmed civilians doubled, with international airstrikes accounting for about half of the casualties. The UN noted a “considerable increase in civilian casualties caused solely by international military forces in Nangarhar province.”

While the international coalition accounted for only 2% of civilian casualties overall, it was behind some of the worst single incidents, including an airstrike on a village near Kunduz that killed 32 civilians, including 20 children.

The UN said the deterioration in protection of civilians from all parties was reinforced by a “pervasive absence of accountability”.

Additional reporting by Mokhtar Amiri in Kabul and Abdurrauf Mehrpoor in Lashkar Gah