At least seven US soldiers were killed when two special forces MH-47 helicopters came under fire during combat operations in eastern Afghanistan.
One of the helicopters was downed; the other was hit but managed to return to base.
"We can confirm that sometime early evening our time last night an MH-47 was fired upon and went down. We have some small numbers of US troops killed," said Pentagon spokeswoman Ms Victoria Clarke.
"We do not know how many may have died as a result of the crash versus small-arms fire," she said.
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Washington sources suggest at least five people were injured.
AFP