(Adds ISAF statement)

By Hamid Shalizi

KABUL, Oct 28 (Reuters) - U.S.-led coalition and Afghan troops killed about 80 Taliban fighters in a six-hour battle following an ambush in southern Afghanistan, the U.S. military said on Sunday.

Taliban fighters opened fire on Saturday with machineguns and rocket-propelled grenades on the joint coalition and Afghan army patrol from a trench system near Musa Qala in Helmand province, the most important town held by insurgents.

"The combined patrol immediately returned fire, manoeuvred, and employed close air support resulting in almost seven dozen Taliban fighters killed during a six hour engagement," the U.S. military statement said.

Such lengthy pitched battles are relatively rare in Afghanistan, where the Taliban prefer to "shoot and scoot" before air strikes can be called in.

But analysts say the insurgents are expected to fight hard to defend Musa Qala, in the north of Helmand, where they are heavily dug in after taking control of the town in February.

A Taliban official in the town denied any insurgents had been killed around Musa Qala and accused foreign forces of dropping bombs on civilians.

The U.S.-led coalition and NATO-led International Security Assistance Force (ISAF) accuse the Taliban of making false accusations of civilian casualties and say foreign troops take every effort to avoid hurting ordinary Afghans.

ISAF said on Sunday it had investigated an air strike in Wardak province on Monday and concluded there was no truth in reports by a local government official who said 11 members of an Afghan family had been killed.

It said the target of the air strikes had been a large group of insurgents setting an ambush for ISAF troops.

TALIBAN HANG THREE

The Taliban hanged three men in Musa Qala on Saturday, accusing them of spying for foreign forces, another Taliban official in the town said. Two were strung up at the entrance to the town and the other in the town centre.

Mainly British troops are engaged in almost daily gun battles further south in the province, an area of harsh, barren desert sliced through by the Helmand River which provides a lush strip of fertile land where more than half the world's opium is grown.

Foreign military forces say they can take back Musa Qala at any time, but do not want to do so until an Afghan civilian administration and security forces are ready to take control of the town.

In the meantime, U.S. and Afghan forces have launched a series of reconnaissance patrols around Musa Qala.

Elsewhere, several Taliban insurgents were killed after an ambush on U.S.-led coalition troops in neighbouring Kandahar province, the U.S. military said.

NATO-led forces are also conducting operations in Helmand and Kandahar, but unlike the U.S.-led coalition force, do not release Taliban casualty figures.

More than 7,000 people have been killed in renewed violence since the Taliban re-launched their offensive against the Afghan government and its Western backers two years ago.

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