The decision to change Russia's official nuclear doctrine is the Kremlin's answer to a reported decision by the administration of U.S. President Joe Biden to allow Ukraine to fire American long-range missiles deep into Russia.

The updated doctrine, which outlines the threats that would make Russia's leadership consider a nuclear strike, said an attack with conventional missiles, drones or other aircraft could be considered to meet these criteria.

It also said any aggression against Russia by a state that was a member of a coalition would be considered by Moscow to be aggression against it by the whole coalition. Commenting on the move on Tuesday, Kremlin spokesman Dmitry Peskov said it was intended to make potential adversaries aware of the “inevitability of retaliation.”

He added that “the Russian Federation reserves the right to use nuclear weapons in the event of aggression using conventional weapons against it and/or the Republic of Belarus.”

“An important element of this document is that nuclear deterrence is aimed at ensuring that a potential adversary understands the inevitability of retaliation in the event of aggression against the Russian Federation or its allies,” Peskov was quoted by CNN as saying.

Just weeks before the November U.S. presidential elections, Putin ordered changes to the nuclear doctrine to say that any conventional attack on Russia aided by a nuclear power could be considered to be a joint attack on Russia.

The Ukraine war, now into its 1,000th day, has triggered the gravest confrontation between Russia and the West since the 1962 Cuban Missile Crisis – considered to be the closest the two Cold War superpowers came to intentional nuclear war.