The United Nations envoy for children and armed conflict Thursday called for a thorough review of procedures after NATO air strikes killed nine children in Afghanistan's eastern Kunar province on Tuesday.

"Children killed in Afghanistan by air strikes is a cause of serious concern," said the Special Representative of the Secretary-General, Radhika Coomaraswamy.

According to media reports, the boys – aged 12 and under – were killed while gathering firewood. NATO commander General David Petraeus has reportedly apologized for the fatalities, which he said occurred due to a communication error about the location of militants.

Coomaraswamy, in a statement issued by her office, welcomed Gen. Petraeus' apology for the incident and his commitment to investigate.

At the same time, she urged a thorough review of procedures "to ensure that all necessary precautions are taken to prevent children from becoming casualties in the complex and volatile situation in Afghanistan."

The Special Representative noted that early last year, the international forces introduced technical directives aimed at better protecting civilians during air strikes, which had resulted in a significant decrease in the number of children killed by pro-Government forces in 2010.