WASHINGTON A U.S. special forces MH-47 helicopter was shot down during combat operations in eastern Afghanistan late Sunday, killing "a small number" of U.S. troops and injuring others, the Pentagon's chief spokesperson said.

"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 U.S. troops killed," Victoria Clarke, the Pentagon spokeswoman, was quoted by AFP.

"We do not know how many may have died as a result of the crash versus small arms fire," she said.