KABUL, Afghanistan — A helicopter carrying international troops crashed Tuesday, killing nine service members in southern Afghanistan where troops are ramping up pressure on Taliban insurgents.It was the worst chopper crash for coalition forces in four years in the rugged country where helicopters are heavily used to transport military troops spread over mountainous terrain with few roads. This year was already the deadliest for international forces since the war began in 2001.One other coalition service member, an Afghan National Army soldier and a US civilian were injured.The nationalities of the service members who died have not been released. So far this year, 525 US and NATO forces have been killed in Afghanistan, surpassing the 504 killed last year.The 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."I was sitting taking my tea," said Nakeemullah, 20, who works transporting livestock in the area. "I heard noise and I went outside to see what happened."I saw a lot of smoke in the sky," said Nakeemullah, who uses only one name. "It was far away for me, but I could see that it was a helicopter and it went down on the backside of the mountain where I couldn't see."NATO said there were no reports of enemy fire in the area. However, Taliban spokesman, Qari Yousef Ahmadi, told The Associated Press by telephone that insurgents shot down the helicopter. The Taliban often exaggerate their claims and sometimes taking credit for accidents.Before this latest event, the worst helicopter crash for coalition forces was in May 2006, a Chinook crashed attempting a nighttime landing on a small mountaintop in eastern Kunar province, killing 10 US soldiers. That followed on a 2005 crash in Kunar that killed 16 Americans. In February 2007, a Chinook helicopter crashed in Zabul, killing eight U.S. personnel.The most recent helicopter crash occurred in southern Kandahar province in August when a Canadian Chinook was shot down, injuring eight Canadians.