Violence against civilians is on the rise in Afghanistan as international forces hand over security to Afghans, the United Nations said in a report on Wednesday, putting the mid-year toll of civilians killed at more than 1,300.

The United Nations said more women and children had become victims of the 12-year-old war. The number of children killed over six months climbed 30 percent compared with the same period last year.

Mounting casualties are reinforcing fears about Afghanistan's ability to tackle the insurgency on its own, after most foreign troops leave next year. The Afghan army faces one of the highest desertion rates in the world and a chronic lack of logistical and medical support.

Insurgents have stepped up attacks on security forces, particularly in areas where international bases have closed, the United Nations said. Both sides have caused the death of civilians.

As in previous years, bombs known as improvised explosive devices (IEDs), remained the single greatest killer, claiming 53 percent more victims than last year, most of them children.

Fighting between security forces and insurgents was the second most significant cause of civilian deaths, the United Nations said, putting the death toll in crossfire at 207.

Overall, almost three-quarters of civilian deaths had been caused by insurgents, who were increasingly targeting civilians seen to be cooperating with the government, the United Nations said.

The rise in deaths of women and children maintained a trend marked last year. Casualties over the six months were up by almost a quarter, including 2,533 reported injuries.

In one of the worst instances, 10 children, most of them infants, were killed in an aerial bombardment that "appeared to serve no clear military/tactical purpose", the United Nations said.

An investigation by the NATO-led force in Afghanistan concluded it was not responsible for the deaths.

STRESS, QUESTIONS

The threat to Afghanistan's civilians has become a significant source of stress in the relationship between President Hamid Karzai and his international backers, particularly when civilian deaths are caused by foreign forces.

But questions have been raised about the ability of domestic forces not only to take on the insurgents but to win the trust and support of people in areas where insurgents operate.

Casualties caused by a security force known as the Afghan Local Police, set up in 2010 to operate in remote, insecure areas, rose more than 60 percent, the United Nations said. Members of the force had been accused of murder, torture and rape.

Many communities, however, reported that they owed an improvement in security to the police.

But the report also noted increased numbers of clashes between unaligned armed groups, a recurrence of the insecurity in the 1990s that enabled the Taliban to take control.

The report also revealed that the U.S. army had launched a fresh inquiry into allegations of war crimes committed between November and February in the strategically important province of Wardak.

That investigation comes on the heels of the arrest of an Afghan translator who worked with U.S. special forces who he said had killed civilians he helped capture. The bodies of as many as 10 civilians were found this year near the military base used by the special forces soldiers.