NATO's chief says Russia could invade Ukraine 'without any warning at all' as Putin tests missile launches

NATO Secretary General Jens Stoltenberg has posed the question that's kept the world on edge for weeks: will Russia attack Ukraine?

Not even those in the Russian government — besides President Vladimir Putin — appear to know the answer, but the fact remains that there has been a steady buildup of Russian troops and military hardware near the Ukraine border; the largest since the end of the Cold War.

"They have all the capabilities in place, Russia, to launch an attack on Ukraine without any warning at all. No one is denying that Russia has all these forces in place," Stoltenberg told CNBC's Hadley Gamble at the Munich Security Conference on Saturday. "The question is, will they launch an attack?"

Over 150,000 Russian troops are stationed at various points along the border with Ukraine. Russian forces have also been posted in Belarus, an ally that lies to the north of Ukraine.

Stoltenberg's comments came as Russia's military launched ballistic and cruise missiles on Saturday in a show of its nuclear readiness. It was part of what the Kremlin called a "planned exercise of the strategic deterrence forces."

"Aerospace Forces successfully launched Kinzhal hypersonic aeroballistic missiles. Ships and submarines of the Northern and Black Sea Fleets launched Kalibr cruise missiles and Zirkon hypersonic missiles at sea and ground targets," the statement from the Russian presidency said Saturday.

"The tasks envisaged during the exercise of the strategic deterrence forces were completed in full, all missiles hit their assigned targets, confirming the specified characteristics."

Moscow has insisted it has no plans to invade Ukraine and its forces in Belarus are there for military drills set to take place in the coming days. The U.S. and its Western allies have warned of severe economic and diplomatic sanctions against Russia should an invasion go ahead.

"Of course there is no certainty about that," Stoltenberg added. U.S. President Joe Biden has issued numerous warnings that an invasion is imminent, much to the mockery of Russia and its allies.

But Stoltenberg added: "NATO allies and the United States have the same assessment, that it's a very high risk for a Russian attack on Ukraine."

Russia's military said in a statement earlier this week that it was pulling back some of its troops to mark the end of their exercises, leading markets to breathe a brief sigh of relief, but Western leaders stress that there is no evidence of a genuine reduction in forces around Ukraine.

Also of concern is "the very threatening rhetoric," the NATO chief added, noting that, "we have seen attempts by Russia to stage a pretext — the Ukraine situation in Donbas or somewhere else — as an excuse for attacking Ukraine. We have seen false accusations about genocide, we have seen accusations of violations of ceasefires in Donbas, and all of this of course adds to the picture that this is a real danger for a Russian attack."

The U.S. has accused Russia of plotting to fabricate an attack by Ukrainian forces as a pretext for the invasion of its neighbor. The White House said in early February that it has intelligence Russia is considering using a staged video of a Ukrainian attack involving actors.

The Kremlin has denied it is preparing any "false flag" operations.

The accusation comes amid a prolonged period of escalated tensions between Russia and Ukraine, with the U.S. and NATO concerned about the unfurling geopolitical crisis.