(Adds police wounded, roadside bomb)

KABUL, July 26 (Reuters) - U.S.-led troops, backed by air power, killed more than 50 insurgents in a battle in Afghanistan's southern province of Helmand, the U.S. military said on Thursday.

There were no casualties among coalition troops in the 12-hour battle with Taliban militants, which finished early on Thursday, it said in a statement. No civilian injuries were reported, it added.

More than 160 insurgents have been killed in Helmand's Musa Qala district since Sunday, the military said.

The Taliban, who are leading an insurgency against the government and foreign troops, could not be reached for comment and because of the remoteness of the region there was no independent verification of the report.

Two residents phoned a Reuters reporter in the south to say that 17 people, 16 of them civilians, were killed in the bombing.

They said up to 30 people were wounded, most of them non-combatants.

Separately, one NATO soldier was killed on Thursday in a clash in southern Afghanistan, the alliance said.

Four policemen, including a commander, were wounded in a Taliban ambush in the north of the country near the town of Baghlan on Thursday, the commander said from his hospital bed.

A roadside bomb exploded near a Canadian convoy just south of the city of Kandahar in southern Afghanistan, but there were no injuries to either soldiers or civilians, Canadian forces said.

Violence has surged in Afghanistan in the past 18 months, the bloodiest period since U.S.-led troops overthrew the Taliban's government in 2001.

Civilian deaths are a sensitive issue for President Hamid Karzai's government and the foreign troops led by NATO and the U.S. military.

More than 330 civilians have been killed in foreign troops operations this year alone in Afghanistan, according to Afghan officials and Western aid workers.

Faced with criticism over perceived lack of economic and reconstruction development, rising crime, rampant corruption and booming illegal drugs, Karzai has warned that civilian deaths would have bad consequences for his government and the troops. (With additional reporting Mirwais Afghan in KANDAHAR)

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