Warning time for Russian attack is going down- NATO

NATO's security general warned on Thursday of a "dangerous moment" for Europe as Russia builds up troops near Ukraine and holds joint military drills in Belarus, but reiterated an offer of talks with Moscow.

Jens Stoltenberg, speaking alongside British Prime Minister Boris Johnson, said he had sent a letter to Russian Foreign Minister Sergei Lavrov offering to discuss more transparency around exercises, as well as nuclear arms control, reports Reuters.

"This is a dangerous moment for European security," Stoltenberg told a news conference with Johnson. "The number of Russian forces is going up. The warning time for a possible attack is going down," he added.

"NATO is not a threat to Russia, but we must be prepared for the worst while remaining strongly committed to finding a political solution," Stoltenberg said.

He said Russia must choose between a diplomatic solution to the crisis over Ukraine or face economic sanctions from the West and an increased military presence of NATO forces in the alliance's eastern countries.

"Russia has a choice: they can either choose a diplomatic solution - and we're ready to sit down - but if they choose confrontation, they will pay a higher price," Stoltenberg said.

"There will be economic sanctions. There will be an increased NATO military presence in the eastern part of the alliance, and the UK is really an important part of that," he admitted.