Nine service members with the international coalition in Afghanistan died Tuesday after their helicopter crashed in the volatile south where troops are ramping up pressure on Taliban insurgents.

Those killed in the crash were not formally identified, but a NATO source in Afghanistan told CBS News Tuesday morning all the those killed were American troops, likely part of a special forces mission.

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The NATO official spoke on condition of anonymity pending the release of official information.

One other coalition service member, an Afghan National Army soldier and a U.S. civilian were injured in the crash and were transported to a military medical center for treatment, NATO said.

Though helicopters more regularly crash because of mechanical issues in Afghanistan, some have been brought down by insurgent fire.

However, NATO said in a statement, “There are no reports of enemy fire in the area.”

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Choppers are used extensively by both NATO and the Afghan government forces to transport and supply troops spread out across a mountainous country with few roads. Losses have been relatively light, despite insurgent fire and difficult conditions, and most crashes have been accidents caused by maintenance problems or factors such as dust.

Tuesday’s crash occurred in northwestern Zabul province, according to a NATO official, who spoke on condition of anonymity because he was not authorized to disclose the location of the crash. Mohammad Jan Rasoolyar, a spokesman for the provincial governor in Zabul, said the helicopter went down in Daychopan district.

In April, three service members were killed when a U.S. Air Force Osprey went down seven miles from Qalat, capital of Zabul, about 200 miles southwest of Kabul. It was the first crash of the costly tilt-rotor aircraft in a combat zone, the U.S. military said. In July 2009, NATO reported that two Canadian troops and a Briton were killed in a helicopter crash in Zabul.

The most recent helicopter crash before this one occurred in southern Helmand province in July, killing two U.S. service members. The Taliban had claimed it had shot it down. NATO said at the time it was investigating.

The deaths raise to 32 the number of international troops killed so far this month in Afghanistan.

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