The number of Afghan civilian casualties has fallen for the first time in five years, dropping by 15 percent in the first half of 2012, the United Nations said Wednesday as a double suicide attack killed three US soldiers.

"This is the first time we have seen a sustained decline in civilian casualties which actually reverses a sustained five year trend of increasing of civilian casualties," UN human rights official James Rodehaver told AFP.

The United Nations said 1,145 Afghan non-combatants lost their lives, mostly in Taliban and other insurgent attacks, between January 1 and June 30 compared to 1,510 for the same period in 2011. Another 1,954 civilians were wounded, it added.

The UN mission in Afghanistan said that marked a 15 percent decline on the 3,654 casualties documented during the first six months of 2011.

Last year as a whole, a record 3,021 civilians died as part of the decade-long war between Taliban insurgents and the NATO-backed Kabul government, the United Nations has said.

The findings come as 130,000 US-led NATO troops prepare to withdraw the bulk of their combat troops from Afghanistan in the next 18 months.

The apparent decline in civilian casualties contrasts to an 11 percent increase in insurgent attacks reported by NATO in the last three months.

And as the Taliban increasingly target homegrown forces, Afghan troops die at five times the rate of NATO soldiers, according to the independent website icasualties.org.

The United Nations said insurgents were responsible for 80 percent of the civilian casualties in 2012, while pro-government forces, which include NATO, were blamed for 10 percent. The remaining 10 percent was attributed to unknown groups.

It said there had been a 53 percent increase in targeted killings of civilians, picked out by insurgents because they work for the Afghan authorities or the military.

In the past, NATO air strikes have sparked huge controversy with President Hamid Karzai's government, but the UN report said civilian casualties from air strikes were down 23 percent compared to the same period in 2011.

Women and children accounted for about 30 percent of this year's casualties -- up one percent from the same period in 2011 -- killed or wounded mostly in Taliban roadside bombings with IEDs, the insurgents' weapon of choice.

The United Nations also highlighted concern about human rights abuses, mostly in the form of "parallel judicial structures" led by the Taliban and other insurgents that meted out punishments that include executions, amputations and lashings.

It said in areas of limited government authority, "anti-government elements" were able to "carry out serious human rights abuses with impunity".

On Wednesday, Afghan and Western officials said a double suicide attack killed three US soldiers in eastern Afghanistan.

The US-led International Security Assistance Force said three of its troops died in an "insurgent attack" in the east.

It did not disclose the nationalities of the soldiers, but Americans serve in Kunar, a flashpoint for Taliban and other Islamist militants on the Pakistani border.

A spokesman for the local government told AFP that three US soldiers died when two suicide attackers approached a group of American soldiers who were on their way from their base to the governor's office in the provincial capital Asad Abad.

"Our information shows that the two attackers approached the US soldiers on foot and detonated themselves one after another," said the spokesman, Wasefullah Wasefy.

A Western security official later confirmed that the dead soldiers were Americans.