Russian President Putin meets with journalists in Tehran
Reuters

Russia has notified the United States about its plans to carry out annual exercises of its nuclear forces, the U.S. government said on Tuesday, a move that Washington said lowers the risk of miscalculation at a time of "reckless" Russian nuclear rhetoric.

The United States has said it expects Russia to carry out test launches of missiles during its annual "Grom" exercises of its strategic nuclear forces, noting in the past it has fired inter-continental ballistic missiles.

Under the New START Treaty, Russia is obliged to provide advance notification of such missile launches, U.S. officials say.

"The U.S. was notified, and, as we've highlighted before, this is a routine annual exercise by Russia," spokesman Air Force Brigadier General Patrick Ryder announced at a news briefing.

Ryder declined to offer further details.

The drills present a potential challenge to the United States and its allies, as Russian President Vladimir Putin has muddied the waters about his intentions after openly threatening to use nuclear weapons to defend Russia in its unraveling invasion of Ukraine.

Russia on Tuesday also took allegations to the U.N. Security Council that Ukraine is preparing to use a "dirty bomb" on its own territory, an assertion flatly dismissed by Western and Ukrainian officials as misinformation and a pretext for escalating the war.

Western officials have expressed confidence in their ability to discern the difference between a Russian drill and any move by Putin to make good on his nuclear threats.

At the U.S. State Department, spokesperson Ned Price stressed the importance of compliance with such notification requirements.

"While Russia engages in unprovoked aggression and reckless nuclear rhetoric, these notification measures do ensure we're not taken by surprise and reduce the risks of misperception," Price said.

With Ukrainian forces advancing into Russian-occupied Kherson province, threatening a major defeat for Moscow, Russian officials phoned their Western counterparts on Sunday and Monday to communicate their allegations about a "dirty bomb."

Ukraine's President Volodymyr Zelenskiy said the allegation showed Moscow was planning such an attack with an explosive device laced with radioactive material, and seeking to blame Kyiv.

But questions are also circulating about whether Moscow might use a lower-yield "tactical" nuclear weapon.

U.S. President Joe Biden warned Moscow on Tuesday that such a move would be an "incredibly serious mistake."

"I'm not guaranteeing you that it's a false flag operation yet, we don't know. But it would be a serious mistake," Biden said.