Russian jets cross into Ukraine airspace

Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, spoke with his Russian counterpart, Gen. Valery Gerasimov, on Thursday and to express “grave concern” over Russia's aggressive military behavior, the Pentagon said in a statement.

“The two military leaders agreed on the need to reduce tension, avoid miscalculation and keep an open line of communication,” according to the statement.

Warren said U.S. officials have let Russian defense ministry officials know that Defense Secretary Chuck Hagel would like to speak to his counterpart, Russia Defense Minister Sergei Shoigu. There has been no response yet, Warren said.

This is the second set of military exercises conducted by the Russians along the border region. The latest exercises were quickly denounced by Hagel, who called them “dangerously destabilizing” and “very provocative.”

If such activities escalate, they will make it more difficult to find a diplomatic solution to the situation in Ukraine, Hagel said, speaking in Mexico City.