WASHINGTON

NATO Secretary General Jens Stoltenberg on Thursday strongly condemned Russia’s "reckless and unprovoked attack on Ukraine," saying it puts at risk countless civilian lives.

"Once again, despite our repeated warnings and tireless efforts to engage in diplomacy, Russia has chosen the path of aggression against a sovereign and independent country," said Stoltenberg in a statement.

His remarks came shortly after Russian President Vladimir Putin announced a special military operation early Thursday in eastern Ukraine’s Donbas region. Following Putin’s announcement, large explosions were reported in Ukraine's capital Kyiv and city of Kramatorsk.

"This is a grave breach of international law, and a serious threat to Euro-Atlantic security. I call on Russia to cease its military action immediately and respect Ukraine’s sovereignty and territorial integrity," said the NATO chief.

"NATO Allies will meet to address the consequences of Russia’s aggressive actions. We stand with the people of Ukraine at this terrible time. NATO will do all it takes to protect and defend all Allies," he added.