NATO Secretary General Anders Fogh Rasmussen on Tuesday said that the Ukraine crisis has amplified the need to strengthen cooperation between NATO, the European Union and other partners.

"We need to train and exercise more together -- for instance, the NATO Response Force and the EU Battle groups -- so that we stand ready for whatever the future may bring," Rasmussen said, arriving for the EU defense ministers talks in Luxembourg.

Accusing Russia's of applying continued military pressure on Ukraine's border, Rasmussen said, "I call on Russia to de-escalate the crisis."

"Russia should stop being part of the problem, and start being part of the solution," he said.