• NATO's secretary general said Russian aggression and use of force is the "new normal" in Europe.
• Jens Stoltenberg made the remarks at a press conference in Brussels on Wednesday.
• "Further Russian aggression against Ukraine would have a high cost," he warned. 

NATO's secretary general said on Wednesday that Russian aggression against Ukraine and the country's use of force are the "new normal" in Europe.

"Moscow has made it clear that it is prepared to contest the fundamental principles that have underpinned our security for decades, and to do so by using force," Jens Stoltenberg said at a press conference in Brussels, after speaking with NATO defense ministers. 

He added: "I regret to say that this is the new normal in Europe."

Stoltenberg's comments come after Russia said it had withdrawn some of its forces from along the Ukraine border — a move that the US and NATO have not been able to verify. 

He said it's unclear "what will happen in Ukraine," but that "the situation has already demonstrated we face a crisis in European security."

"Further Russian aggression against Ukraine would have a high cost," he said.