Ukraine did not immediately confirm the use of the ATACMS, which would be the first since U.S. President Joe Biden gave the green light for Kyiv to fire them into Russia after months of lobbying from President Volodymyr Zelenskiy.

"Last night at 3.25 (0025 GMT) the enemy struck a facility in the Bryansk region with six ballistic missiles. According to confirmed data, American-made ATACMS operational-tactical missiles were used," the Russian defence ministry said in a statement.

It said Russian air defences shot down five missiles and damaged one, whose fragments fell on a military facility.

The ministry said this caused a fire that was quickly extinguished, and there were no casualties or damage. Reuters could not independently confirm details of the incident.

Russia has said the U.S. decision to approve such attacks was reckless and will prompt it to respond.

President Vladimir Putin on Tuesday approved an updated nuclear doctrine lowering the threshold that would prompt Russia to consider using nuclear weapons.

The new policy says any conventional assault on Russia by a non-nuclear power supported by a nuclear power will be considered to be a joint attack.

Any mass aerospace attack with aircraft, cruise missiles and unmanned aircraft that crossed Russia's borders could also trigger a nuclear response, it says.