NATO and Russia are set to separately hold long planned exercises of their nuclear forces at a time of huge tension as Russia continues its war on Ukraine.

The Pentagon and the US intelligence community are watching for any unexpected or unusual movements of Moscow's nuclear weapons during Russia's exercise, which is expected to take place before the end of the month, according to several US officials.

"We believe that that Russian nuclear rhetoric and its decision to proceed with this exercise while at war with Ukraine is irresponsible. Brandishing nuclear weapons to coerce the United States and its allies is irresponsible," a senior defense official told CNN.

The Russian exercise called Grom, which roughly translates into thunder, is conducted every year, according to the US. "We anticipate the exercise will span several days. It'll include actions within the normal bounds of what Russia has done in the past. It'll include live missile launches and a deployment of strategic assets," said John Kirby, Coordinator for Strategic Communications at the National Security Council.

Though the Russian exercise is routine it comes after President Joe Biden issued a stark warning earlier this month about the danger of President Vladimir Putin's nuclear threats as Moscow continues to face military setbacks in Ukraine.

"First time since the Cuban missile crisis, we have a direct threat of the use (of a) nuclear weapon if in fact things continue down the path they are going," Biden warned during remarks at a Democratic fundraiser in New York.

He added: "I don't think there's any such thing as the ability to easily (use) a tactical nuclear weapon and not end up with Armageddon."

After Biden's remarks, administration officials stressed that the US still has seen no evidence that Putin is moving toward using Russia's nuclear capability, nor is there any intelligence showing he's decided to do so.

The tensions over Ukraine means there will be even more scrutiny on the Russian exercise. The US constantly monitors Russian nuclear assets, but the Pentagon will be watching the exercise for any sign Russian strategic forces or nuclear weapons movements are anything other than routine and expected, officials told CNN.

The exercise is expected to focus on strategic weapons, meaning tests of ballistic missile systems that Russia would be required to provide advance notice of under treaty obligations.

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NATO and US officials have said they are confident they will be able to accurately monitor any Russian nuclear activity during the exercise. "We will monitor that, as we always do. And of course, we will remain vigilant not least in light of the veiled nuclear threats and the dangerous nuclear rhetoric we have seen from the Russian side," said NATO Secretary General Jens Stoltenberg on Thursday.

On Monday, NATO will begin its annual nuclear exercise known as Steadfast Noon, with the US among the 14 nations participating. It's been conducted annually for over a decade, according to the Pentagon.

The exercise includes fighter jets capable of carrying nuclear warheads but there will be no live weapons aboard. The US will provide B-52 bombers flying from Minot Air Base in North Dakota. The major exercise area will be more than 625 miles from Russia. The goal is to ensure NATO's nuclear deterrent remains "credible, effective, safe and secure" the defense official said.

According to NATO there will be up to 60 aircraft involved including advanced fighter jets, surveillance and tanker aircraft. Flights will take place over Belgium, the UK and the North Sea.

- by Barbara Starr, CNN