REUTERS

"The ceasefire must be observed, heavy weapons should be withdrawn, and we call on Russia to stop supporting the separatists and withdraw heavy weaponry from the area" he said.

"Actions speak louder than words," said Stoltenberg, adding that Russia's "more aggressive behavior," was a challenge for NATO.

"Now is the time to act... there is urgency when it comes to fulfilling the Minsk agreement," he said.