Russian warplanes have entered Ukrainian airspace several times in the last 24 hours, the Pentagon announced Friday.
U.S. officials called on Russia to cease the operations, said Army Col. Steve Warren, a Pentagon spokesman.
“We call upon the Russians to take immediate steps to de-escalate the situation,” Warren said.
Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, spoke with his Russian counterpart on Thursday, but details of their conversation were not released. Defense Secretary Chuck Hagel has tried, without success, to contact Russia’s defense minister.