At least 13 civilians were killed, mostly children, in an air strike by "international forces" in the northern Afghan city of Kunduz late last week, the United Nations said yesterday.

The strike happened between late Friday and early Saturday in support of ground operations conducted by pro-government forces fighting against Taliban militants in the area.

"Initial fact-finding indicates that 10 of those killed were children, part of the same extended family whom were displaced by fighting elsewhere in the country," the UN mission in Afghanistan said in a statement.

The US is the only member of the international coalition in Afghanistan that provides air support in the conflict.

A NATO spokesperson told AFP the coalition was investigating the claims.

The deaths come as ordinary Afghans continues to bear the brunt of the war in Afghanistan, with more civilians killed in the Afghan war in 2018 than during any other year on record, according to a UN report.

The uptick in violence in 2018 coincides with a significant increase in the number of deaths caused by the "deliberate targeting of civilians", according to the report, mostly stemming from suicide attacks by insurgents allied with the Taliban or Islamic State (IS).