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2 U.S. Marines Killed in Afghan Fighting

The U.S. military said Tuesday that two Marines had been killed in Afghanistan's southern Helmand province, the latest casualties as American forces seek to oust Taliban militants from their stronghold in the world's opium producing capital.

A statement released by the coaltion military force in Afghanistan said the troops were killed in a "hostile incident" on Monday.

Meanwhile, a civilian helicopter contracted by the U.S. military in Helmand crashed killing six people, according to NATO officials.

About 4,000 U.S. Marines have recently joined the fight in Helmand province - the first part of President Obama's intended surge of forces into the country to quell violence which has persisted since the Taliban government was toppled in 2001.

Military spokeswoman LTCdr Christine Sidenstriker told CBS News' Fazul Rahim there were casualties in the helicopter crash, but she could not provide any further details on how many people were injured or killed.

A coalition military source, speaking on condition of anonymity because the information had not yet been made public, told CBS News that neither the helicopter nor its crew were American.

Helmand province official Fazel Haq told the Associated Press the white helicopter crashed and caught fire around daybreak Tuesday in Sangin district in the country's south.

A spokesman for the NATO-led force said six civilians on board were killed and an Afghan national on the ground was hurt. He could not be identified because he was not the media office's top spokesman.

Sidenstriker would not say what caused the helicopter to crash on Tuesday, but she did not rule out the possibility of enemy fire.

In a text message sent to CBS News' Sami Yousafzai, a Taliban commander claimed Tuesday that militants had shot down a helicopter in Helmand province. The claim could not be verified, but the timing and approximate location matched the crash confirmed by Sidenstriker.

The chief of Helmand's Sangin district told Reuters news agency he saw the helicopter on fire before crashing to the ground.

"It was in the sky on fire and then went down," Fazlul Haq told the news agency.

At least 107 U.S. troops have been killed in Afghanistan this year - a staggering pace for American casualties that could easily pass the death toll of 2008, when 151 service members were killed in the country.

On Monday, the American military reported one service member's death as a result of enemy fire during a vicious fight in the town of Bargh-e-Matal, in the eastern province of Nuristan.

CBS News correspondent Mandy Clark was with American troops as they found themselves surrounded by Taliban militants perched on high hills. Clark's exclusive report from the battle for Bargh-e-Matal can be seen below: