The State Department said that Russia complied with agreements to inform the United States of tests of intercontinental ballistic missiles and submarine-launched ballistic missiles.

"This is a routine annual exercise by Russia," State Department spokesman Ned Price told reporters.

"So 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.

The US and Russian defense chiefs have spoken twice in the past week in rare contact amid soaring tensions since Moscow's invasion of Ukraine on February 24.

The United States, France and Britain said that Russian Defense Minister Sergei Shoigu raised the prospect of Ukraine detonating a "dirty bomb" with nuclear material -- raising Western concerns that Moscow may be preparing a false-flag operation.

"We're concerned because Russia has a pattern of accusing others of that which it ultimately itself is planning," Price said, calling Moscow's remarks "irresponsible."

But he reiterated that the United States had no indication that Russia was preparing to use nuclear weapons.