Russia claims Ukraine used American-made missiles in an attack, hinting at a potential nuclear response.

• Moscow signaled to the West that it's ready for a nuclear confrontation.
• Early Tuesday, Russian military facilities in the Bryansk border region were targeted by missiles, according to Ukrainian news outlets.

After receiving permission to attack Russian territory, Moscow signaled to the West that it's ready for a nuclear confrontation and quickly acted on that greenlight by using U.S.-made long-range missiles.

Ukrainian news outlets reported early Tuesday that the U.S.-made ATACMS missiles were used to attack a Russian military facility in the Bryansk border region after Kyiv was reportedly given the go-ahead by Washington Sunday.

The Ministry of Defense in Russia confirmed that Ukrainian forces had attacked a facility in the Bryansk region using six American-made ATACMS missiles. The ministry stated that air defense missile systems had successfully shot down five of the missiles and caused damage to another.

The military facility in the Bryansk region experienced a fire caused by fragments that fell on its technical territory. The fire was quickly put out, and there were no casualties or damage, according to the ministry.

The reports were not confirmed by CNBC and Ukraine's government has not issued a statement regarding the attack.

A national security official confirmed the strike in Bryansk, but did not specify which weapons were used, according to the Kyiv Post news outlet.

Russia has intensified its warnings to the West against allowing Ukraine to use long-range weapons to attack it directly, as Russian President Vladimir Putin signed a decree on Tuesday approving an updated nuclear doctrine that expands the circumstances under which Russia can use nuclear weapons.

Any aggression against Russia by a non-nuclear state, if it's supported by a nuclear power, will be considered as a joint attack, according to the updated document outlining the conditions in which Russia can use nuclear weapons.