Mounting casualties are reinforcing fears about Afghanistan's ability to tackle the Taliban insurgency on its own, after most foreign troops leave next year

* Casualties in Afghanistan up by 23 percent compared to 2012:U.N. report

* Women and children increasingly the victims in 12-year-old war

* Insurgents target areas already vacated by international forces

By Jessica Donati

KABUL, July 31 (Reuters) - Violence against civilians has risen by almost a quarter in Afghanistan as international forces hand security to Afghans, the United Nations said in a report on Wednesday, with insurgents striking in areas where troops have already left.

The report, presented by the Human Rights Director for the U.N. in Afghanistan, said the number of dead and injured civilians had increased by 23 percent in the first six months of 2013, compared to the same period last year.

Women and children are increasingly the victims of the 12-year-old war, the report said, noting a 30 percent leap in the number of children killed. The total civilian death toll stood at more than 1,300, with 2,533 reported injuries.

Mounting casualties are reinforcing fears about Afghanistan's ability to tackle the Taliban 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.

"The stepped-up transition of security responsibilities from international military forces to Afghan forcse and closure of international forces' bases was met with increased attacks by anti-government elements...," Georgette Gagnon said in presenting the report.

The intensified attacks occurred "mainly at checkpoints, on strategic highways, in some areas that had been transitioned and in districts bordering neighbouring countries".

Figures released in 2012 showed a decline in civilian deaths compared to the previous year.

The U.N. report said bombs, or 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 had emerged as the second most significant cause of civilian deaths, with the report putting the death toll in crossfire at 207.

Both sides were responsible for civilian deaths, but the report said almost three-quarters were caused by insurgents, who were increasingly targeting civilians seen to be cooperating with the government, the report said.

Gagnon urged insurgents to "stop deliberate targeting and killing of civilians and withdraw orders that permit attacks" on legal personnel, clergy and government workers.

But the Taliban said anyone supporting President Hamid Karzai's Western-backed government was a legitimate target.

"We never consider those people as civilians who are directly involved in our country's occupation and work with sensitive organs of the enemy," Taliban spokesman Zabihullah Mujahid said in an emailed statement.

WOMEN, CHILDREN IN FIRING LINE

The rise in deaths of women and children maintained a trend marked last year.

In one of the worst instances, 10 children, most of them infants, were killed in an aerial bombardment in the eastern province of Kunar 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, though human rights groups and the U.N. have questioned that finding.

The threat to civilians has become a significant source of stress in relations between Karzai and his 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. Force members 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.

(Editing by Robert Birsel and Ron Popeski)

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