Defense Secretary Chuck Hagel said Washington is aware that Russia had pulled back thousands of troops from the Ukrainian border.

However, he said there are still thousands of troops left. According to Pentagon officials, Russian troops remain near the border, but less than 40,000 that were deployed before.

Last week  Vlaidmir Putin ordered to pull troops back after drills near the Ukrainian border. Putin ordered Defense Minister Sergey Shoygu to return troops participating in drills in Rostov, Belgorod and Brytansk regions back to the places where they are permanently deployed, Kremlin said in a statement.