Defense Secretary Chuck Hagel said he sees no evidence Russia has withdrawn troops massed on its border with Ukraine.

“They’re not leaving, as far as we can tell,” Hagel said in an interview broadcast today on ABC’s “This Week” program.

The U.S. and European Union accuse Russian President Vladimir Putin of trying to destabilize Ukraine in a push to increase his sway in territories that once comprised the Soviet Union. Putin has arrayed a force of as many as 40,000 troops on Ukraine’s eastern border, according to the North Atlantic Treaty Organization.

“Russia continues to isolate itself for a short-term gain,” Hagel said in the interview taped yesterday. Asked if Russia is an enemy of the U.S., Hagel said, “we’re not at war with Russia.”

Asked about U.S. help to Nigeria in the search for more than 200 girls abducted from a school last month by the Islamist militant group Boko Haram, Hagel said, “it’s going to be very difficult.”

“We’re going to bring to bear every asset we can possibly use,” he said of U.S. efforts. “There’s no intention at this point to put any American boots on the ground.”