Allies see day of heavy loss in Afghanistan U.S. Marine CH-53 copters, like the one that crashed Thursday, sit on a tarmac in Afghanistan last year. NEW: Six U.S. Marines were killed in the helicopter crash, a U.S. military official says NEW: French troops killed by an Afghan soldier were unarmed at the time, an official says NATO chief Rasmussen pays tribute to four French soldiers killed in Afghanistan Kabul, Afghanistan (CNN) -- Allied forces have suffered a day of heavy losses in Afghanistan in a helicopter crash that killed 6 U.S. Marines and an attack that killed four French service members and raised the prospect of France withdrawing its troops early. The Marines died after their CH 53 helicopter crashed in Helmand province, a U.S. military official said. The NATO-led force reported no enemy activity in the area, but the Taliban claimed credit for bringing down the copter. Separately, an Afghan soldier killed four French service members and injured 15 others, one critically, in eastern Afghanistan, French officials said. French President Nicolas Sarkozy said he was suspending French training operations and combat help as a result. "The French army is not in Afghanistan to be shot at by Afghan soldiers," he said. France could bring its troops back early from Afghanistan if the necessary security is not restored, Sarkozy said. France has 3,935 troops in Afghanistan, according to the NATO-led International Security Assistance Force. Sarkozy will send French Defense Minister Gerard Longuet to Afghanistan, he said. A French official told CNN the French troops were unarmed as they were inside their base, conducting normal training operations with their Afghan partners. The official, who was not authorized to speak to the media, said 15 soldiers were injured. Responding to the shooting last month, Sarkozy stressed his country's "determination to continue working within the International Security Assistance Force to restore peace and stability in that country and contribute to its development."