Gen. Ray Odierno, the outgoing Army chief of staff, said Wednesday that Russia is the top military threat to the U.S.
"I believe Russia is the most dangerous," he said at a Pentagon briefing.
"And they have shown some significant ability in Ukraine to do operations that are fairly sophisticated, and so for me, I think we should pay a lot of attention to that," he added.
Odierno's comments come as defense officials suspect that Russia is behind last month's cyber attack of the Joint Chief of Staff's unclassified email server. They also come as the U.S. is continuing to support Ukrainian forces as they battle Russian-backed separatists and Russian forces in Eastern Ukraine.
The four-star general said he is also "greatly" concerned by the prospect of Russia violating the sovereignty of Baltic states that are members of NATO, which would require the U.S. military to come to their defense under Article V of the organization's founding treaty.
Russia is "constantly assessing the reaction of NATO to any of their actions," Odierno said.
"What I worry about is miscalculation — that they perceive maybe that NATO might not be as concerned, and they make a mistake and miscalculate and do something that violates Article V of our NATO agreement, so that's something that greatly concerns me," he continued.
Odierno said the U.S. had to increase its ability to move quickly to the region if needed, and increase interoperability with other NATO forces.
"A true deterrent is one where people are worried that if they do conduct operations, that there will be some level of response," he said.
Odierno's assessment echoes those made by other military chiefs. Last month, Gen. Joseph Dunford, the outgoing Marine Corps commandant and incoming chairman of the Joint Chiefs of Staff, told senators that Russia posed the greatest national security threat.
Odierno is retiring this month after a 39-year career in the Army. He spent much of the last decade commanding forces in Iraq.