More than 4,000 U.S. Army troops who were deployed to Europe on a temporary basis will now have their tour of duty extended - likely for several weeks - as part of the U.S. effort to reassure eastern European allies during the current crisis in Ukraine, CNN reported.

"I don't want to speculate on a timeline, but be assured it will only be for as long as they are needed," John Tomassi, a spokesman for the Army in Europe, told CNN in an email.