President Vladimir Putin said Russia will revise its nuclear doctrine to include a response to “aggression” by non-nuclear states that is supported by other nuclear powers.

“Aggression against Russia by any non-nuclear state, but with the participation or support of a nuclear state, is proposed to be considered as a joint attack on the Russian Federation,” Putin said in televised comments to Russia’s Security Council on Wednesday.

The decision comes after Putin earlier this month warned the U.S. and European countries against allowing Ukraine to strike deep inside Russia using Western long-range high-precision weapons. Russia would make “appropriate decisions” based on the new threats, he said at the time.

The U.S. hasn’t announced any decision to permit attacks so far despite pleas from Ukrainian President Volodymyr Zelenskyy that his military be allowed to conduct strikes against airfields and military installations deeper into Russia. Ukraine wants to use British Storm Shadow cruise missiles to carry out the attacks, guided by U.S. navigational data.

Putin issued his warning as world leaders are gathered in New York for the United Nations General Assembly.

He said Russia would consider resorting to nuclear weapons “upon receipt of reliable information that there was a massive launch of air and space weapons and that they crossed our state border. I mean strategic and tactical aircraft, cruise missiles, drones, hypersonic and other aircraft.”

Russia would also defend its ally Belarus with nuclear weapons if necessary, he said.

Russia last updated its nuclear doctrine in 2020. It currently allows for the use of nuclear weapons in response to an existential threat, or in retaliation for the use of weapons of mass destruction against Russia.