Russian aggression against Ukraine will have severe costs, NATO's Stoltenberg says

U.S. President Joe Biden, European leaders and NATO stand united in their warning to Moscow that a Russian attack on Ukraine will provoke a tough response, NATO Secretary-General Jens Stoltenberg said late on Monday.

"We agree that any further aggression by Russia against Ukraine will have severe costs," Stoltenberg said on Twitter after an online meeting with Biden, and the leaders of France, Germany, Italy, Poland, Britain and the European Union.