The Russian Defense Ministry said Friday it will conduct massive military drills involving its nuclear forces, a move that could further raise tensions at a time when the West is fearing a Russian invasion of Ukraine.

The United States and its allies in Europe and elsewhere are warning of the heavy economic and other consequences Russia will face for any military aggression against its neighbor country, and are calling for a diplomatic solution to the Russia-Ukraine standoff.

But there have been no signs of a breakthrough so far.

The Russian Defense Ministry said the exercises for its strategic deterrence forces will take place Saturday, overseen by Russian President Vladimir Putin. They will include launches of ballistic and cruise missiles, according to Russian media.

Tensions are running high as Russian troops have been arrayed along Ukraine's borders, with forces positioned within Russian territory as well as in Belarus, which has close ties with Moscow, and in Crimea, annexed from Ukraine by Russia in 2014.

Currently, Russia is likely to have amassed between 169,000 and 190,000 military personnel near Ukraine, as compared with about 100,000 on Jan. 30, according to a statement from Michael Carpenter, U.S. ambassador to the Organization for Security and Cooperation in Europe.

He criticized the buildup as "the most significant military mobilization in Europe" since World War II and doubled down on the U.S. assertion that Moscow is seeking to create a pretext to justify an invasion into Ukraine.

The Russian government may stage a fabricated attack by Ukrainian military against Russian territory, or against Russian-speaking people in separatist-controlled territory, to justify military action against Ukraine, he said.

While denying any intention to invade the former Soviet republic, Moscow has been asserting that its security is under threat with the North Atlantic Treaty Organization's eastward expansion and the possibility of Ukraine's membership of the alliance.

Concerns are now growing in particular over the situation in eastern Ukraine -- the Donetsk and Luhansk regions, collectively known as the Donbas and partially controlled by Russia-led forces since 2014.

Ukrainian forces have been fighting pro-Russian separatists in these regions. As clashes continue, a kindergarten in eastern Ukraine was among the civilian structures to be shelled recently, with the two sides blaming each other for the attack.

On Friday, the Russian-backed separatists said they planned an evacuation of residents to the Russian side due to fears of a military operation by Ukraine, in what can be seen as part of efforts to paint Ukraine as the aggressor.