He declared that a conventional attack by any nation supported by a nuclear power will be considered a joint attack on Russia.

Vladimir Putin has approved changes to Russia’s nuclear doctrine, setting out new conditions under which the country would consider using its arsenal. The doctrine now says an attack from a non-nuclear state, if backed by a nuclear power, will be treated as a joint assault on Russia.

By Guy Faulconbridge MOSCOW (Reuters) -Russian President Vladimir Putin issued a warning to the United States on Tuesday, lowering the threshold for a nuclear strike just days after the administration of Joe Biden reportedly allowed Ukraine to fire American missiles deep into Russia.