Last Updated Dec 17, 2013 11:30 AM EST
It was not immediately clear whether the six died in the hard landing or in the subsequent attack on their position.
One person on board the aircraft was injured and survived, two U.S. defense officials said on condition of anonymity because they were not authorized to speak on the record.
A statement issued by the NATO international military coalition said the crash was under investigation and that there was no insurgent activity in the area. In Washington, an official originally said the helicopter had experienced engine failure before the crash, but later said that it was unclear whether that was the case.
The deputy governor of southern Zabul province, Mohammad Jan Rasoolyar, said a NATO helicopter crashed in the remote district of Shajau and U.S. officials later confirmed that Zabul was the location of the U.S. crash.
The U.S.-led international military coalition confirmed the deadly crash but said there were no initial reports of fighting or insurgent activity in the area at the time.
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The U.S.-led international coalition has service members from several countries deployed in the south.Taliban spokesman Qari Yousuf Ahmadi in southern Afghanistan claimed in a message sent to news organizations that militants had shot down the helicopter while it flew at low altitude.
Neither U.S. nor NATO officials immediately confirmed the cause of the hard landing. The Taliban often exaggerates its claims of successful operations.
This year, 109 members of the U.S. military have died in Afghanistan, out of a total of 139 members of the coalition.
The death toll has dropped significantly since the coalition handed over responsibility for security to Afghan forces last summer and coalition troops are now training and assisting.
By comparison, 394 foreign troops died last year, including 297 Americans.
Last week, Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said the U.S. has no intention to renegotiate a security deal with Afghanistan and that a full withdrawal of U.S. forces from the country at the end of 2014 could reverse gains made by the fledgling Afghan forces in their war against the Taliban.
Dempsey told reporters that although he is not yet planning a so-called "zero-option" to remove all U.S. forces at the end of 2014, a failure to sign the deal it could make it an "unfortunate possibility."
"Face the Nation" earlier this month, Defense Secretary Chuck Hagel warned that a U.S. pullout from Afghanistan at the end of 2014 was entirely possible if Karzai continued to refuse to sign the security agreement.
The U.S. wants it signed by Dec. 31, but Afghan President Hamid Karzai has so far refused to do so. It could keep thousands of U.S. troops here for up to a decade.
The agreement aims to help train and develop the Afghan National Security Forces, and allow for a smaller force to go after stubborn remnants of al-Qaida and other groups that Dempsey said still pose a threat to regional and global security.
Afghan forces were holding their ground, he said, but still need help.
Without a foreign presence, he said "the development of the security forces will be impeded, will be slowed, and in some parts of the country I suspect could be reversed."
After a year of negotiation, a deal was struck on the agreement last month and Karzai presented it to a national assembly known as a Loya Jirga for approval. The assembly not only endorsed the deal but demanded that Karzai sign it by the end of this month - which would have complied with an American request to allow time for planning a post-2014 presence.
"What was very clear is that over the course of an exhausting, really, negotiation over many months there was a text that was agreed upon. And that text was considered to be closed, at some point, and presented to the Loya Jirga," Dempsey told reporters at this base north of the capital. "It's not our intention to reopen the text and to renegotiate that which had been already discussed."
Karzai says he wants his successor to sign it after the April 5 elections and has added new conditions since it was brokered. He says will sign only if the U.S. ends airstrikes and raids on Afghan homes and does more to help broker peace with the Taliban.
He has also lashed out at the United States, accusing it of making threats.