The U.S.-led international coalition rejected a United Nations rights group's concern about reports that U.S. military strikes have killed hundreds of children in Afghanistan during the past four years, saying they are "categorically unfounded."

The statement by the International Security Assistance Force came a day after the Geneva-based UN Committee on the Rights of the Child said the casualties were "due notably to reported lack of precautionary measures and indiscriminate use of force."

The coalition also dismissed that claim, saying that it takes special care to avoid civilian casualties.

The coalition said the number of children who died or were wounded from air operations dropped by nearly 40 per cent in 2012 compared with the year before, although it did not give specific figures.

The UN was reviewing a range of U.S. policies affecting children for the first time since 2008. The release of the report coincides with an intensifying debate in Washington over U.S. policy on drone targeting and airstrikes.

CIA director-designate John Brennan faced a Senate Intelligence Committee confirmation hearing on Thursday. His defence of drone strikes to kill terror suspects, including Americans, is causing key lawmakers to consider lifting secrecy from what has become an important weapon in the fight against al-Qaida.

UN Secretary General Ban Ki-moon's special representative said the number of child casualties blamed on airstrikes doubled in 2011. (Canadian Press)

In its report, the UN committee told the United States to "take concrete and firm precautionary measures and prevent indiscriminate use of force to ensure that no further killings and maiming of civilians, including children, take place." Human rights and civil liberties groups applauded the findings.

The UN committee referred to "hundreds" of children killed since 2008 and expressed alarm that the figure had "doubled from 2010 to 2011."

It didn't provide specific numbers, but a report to the UN Security Council last April by Secretary General Ban Ki-moon's special representative for Children and Armed Conflict said the number of child casualties blamed on airstrikes conducted by international and allied Afghan forces doubled compared with the last reporting period, with 110 children killed and 68 injured in 2011.

Report disputed as 'categorically unfounded'

The international coalition acknowledged U.S. forces are sometimes responsible for civilian deaths "despite all efforts to avoid them," but said the overall number of civilian casualties declined by 49 per cent in 2012 compared with the previous year.

It also cited an August report from the UN mission in Afghanistan stating that the vast majority of Afghan civilian deaths are caused by the insurgency.

"The UN Committee on the Rights of the Child's concerns about reports of the death of hundreds of children as a result of attacks and airstrikes by the U.S. military in Afghanistan are categorically unfounded," the coalition statement said.

"Equally unsubstantiated is their assertion that U.S. forces use indiscriminate force during their operations. Finally, the committee's assertion that U.S. troops do not exercise precautionary measures is entirely false."