* NATO investigates whether its troops killed five civilians
* Insurgents responsible for 76 pct of casualties
* Casualties caused by foreign, Afghan forces down 18 pct (Recasts with civilian casualties in Helmand province)
By Jonathon Burch
KABUL, Dec 21 (Reuters) - NATO-led forces said on Tuesday they were investigating whether their troops had accidentally killed five Afghan civilians, as a U.N. report said civilian casualties had risen 20 percent in the first 10 months of 2010.
The United Nations said more than three-quarters of the civilian casualties up to October 2010 had been killed or wounded as a result of attacks by insurgents.
However, civilian casualties caused by U.S. and other foreign forces have long caused friction between the Afghan government and its Western backers. Military commanders have sought to tighten engagement rules, including the use of air strikes.
The NATO-led International Security Assistance Force (ISAF) said five civilians were found dead after its troops came under fire from a compound in Sangin in southern Helmand province earlier on Tuesday.
ISAF said its forces had responded with "direct and indirect" fire -- the latter usually meaning artillery or mortar rounds. The five dead civilians were discovered during a battle damage assessment after the engagement, it said.
"This is a tragedy. We are aware that insurgents purposefully stage attacks against friendly forces using innocent civilians&${esc.hash}39; homes," ISAF spokesman Lieutenant Colonel Patrick Hynes said in a statement.
The southern provinces of Helmand and Kandahar, both Taliban strongholds, have been the epicentre of a renewed surge against insurgents over the past 18 months, with Sangin one of the main battlefields.
"ANTI-GOVERNMENT ELEMENTS"
Violence across Afghanistan is at its worst since the Taliban were ousted by U.S.-backed Afghan forces in late 2001, with military and civilian casualties at record levels despite the presence of about 150,000 foreign troops.
More than 700 ISAF troops have been killed so far in 2010, by far the deadliest year of the war.
In a quarterly report on Afghanistan this month, the United Nations said there were 6,215 civilian casualties from conflict-related incidents, including 2,412 deaths and 3,803 injuries, between January and the end of October this year.
The Taliban and other insurgents, described in the report as "anti-government elements", or AGEs, were responsible for 76 percent of the deaths or injuries suffered by civilians, up a quarter on the same period for last year.
"Civilians continued to bear the brunt of intensified armed conflict as civilian casualties, including deaths and injuries, increased by 20 percent in the first 10 months of 2010," U.N. Secretary-General Ban Ki-moon said in the report.
Insurgent suicide attacks and homemade bombs caused 998 deaths -- 55 percent of the total attributed to AGEs -- and wounded 2,062 civilians, or 70 percent of the total attributed to AGEs, the report found.
Deaths and injuries caused by "pro-government forces", which includes U.S. and NATO troops as well as Afghan army and police, accounted for 12 percent of all civilian casualties, an 18 percent drop on the same period last year, the report said.
Of the 742 civilian casualties attributed to pro-government forces, air strikes caused the largest number, including 162 deaths and 120 injuries, it said.
A report last month by around 30 aid groups said while civilian casualties caused by foreign and Afghan forces had decreased over the past two years -- mainly due to a fall in air strikes -- an increase in the use of air power in recent months risked reversing those gains. [ID:nSGE6AH067]
U.S. forces had dropped 2,100 bombs or missiles from June through September, almost 50 percent more than the same period last year, that report said.
Civilian deaths caused by foreign and Afghan troops in October had also increased by 11 percent on the same month last year, it said, citing foreign military figures.
(Editing by Paul Tait) (For more Reuters coverage of Afghanistan and Pakistan, see: http://www.reuters.com/news/globalcoverage/afghanistanpakistan)
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