“Its purpose is really essentially to train our allied forces so that we are ready and prepared, and we ensure the safety and security of our nuclear capability,” she told reporters.

Following the previous NATO exercises, Moscow sent a letter to the alliance threatening to hit allied territory and mentioning the use of its nuclear arsenal — a move that NATO Secretary-General Mark Rutte publicly rebuked last week.

Tensions are rising as European countries accuse Russia of sabotage and growing so-called hybrid attacks across the continent. 

“Our intention is to really keep things calm,” said a senior NATO official, who was granted anonymity to speak freely. Russian officials “keep ratcheting up this mood of tension and we are going to keep trying to calm the mood.”

U.S. Col. David Bull, chief of NATO’s nuclear operations, said the exercise has garnered “similar” participation to previous years and involves everything from a “simulated alert to [a] live flight exercise” — but “no live nuclear weapons.” 

Russia’s embassy to Belgium didn’t immediately respond to a request for comment.