Vladimir Putin escalated his nuclear threats against the West on Wednesday, saying that any attack on Russia using conventional weapons supported by a nuclear power would now be perceived as a joint strike.

The Russian president told his security council that he needed to “correct” the Kremlin’s nuclear doctrine to permit a retaliatory nuclear strike in the event of a conventional missile attack on Russia.

“Aggression against Russia by any non-nuclear state, but with the participation or support of a nuclear state, is treated as a joint attack on the Russian Federation,” he said.

Previously, Russia’s nuclear doctrine had only allowed it to launch a nuclear strike after a direct attack by an enemy armed with nuclear weapons. Ukraine does not have any nuclear missiles.

Putin said that the “emergence of new sources of military threats and risks for Russia” meant that he had no choice but to update Russia’s nuclear doctrine.

Although he did not name Ukraine, the warning appears to be aimed at Volodymyr Zelensky, who is due to meet Joe Biden at the White House on Thursday to push for permission to fire US-made long-range missiles at Russia.

Sir Keir Starmer has also been putting pressure on Mr Biden to allow British Storm Shadow missiles to fire at Russian targets, rather than in occupied parts of Ukraine.

Putin recently said that he would regard it as an act of war by Nato if it allowed Ukraine to fire Western-made long-range missiles at Russia. Other senior Kremlin officials have also said that Russia could respond with a nuclear missile strike.

“We will consider this possibility on receiving information about a massive attack by air-space weapons that crosses our state border,” Putin said on Wednesday. “I mean strategic and tactical aircraft, cruise missiles, drones, hypersonic and other aircraft.”

He also said that Russia’s new nuclear doctrine would cover Belarus, a key ally.

Putin and other top Kremlin officials have regularly threatened to carry out a nuclear strike because of Western support for Ukraine since it invaded in 2022.

Russia has moved nuclear-capable missiles to Belarus for the first time since the end of the Cold War and tested several of its largest nuclear-capable missiles, but analysts have questioned whether Putin is really prepared to order a nuclear attack.

It is also thought that China, Russia’s most important ally, has told Putin that it would not tolerate a nuclear strike by the Kremlin.

Pavel Podvig, a senior researcher at the United Nations Institute for Disarmament Studies, said that although Putin had tweaked Russia’s nuclear doctrine, he had left the rules vague, potentially allowing him to avoid ordering a nuclear missile strike.

“Should this be an aggression of the kind that threatens the very existence of the state? There is deliberate ambiguity here,” he said.

Ukrainian commentators were more bullish and said that Putin was bluffing as he had done several times previously.

“We need to remember one thing. Whenever Putin starts talking about nuclear weapons, that means that Russia is not doing that well,” Anton Gerashchenko, a Ukrainian analyst and former deputy interior minister, said. 

Mr Zelensky has repeatedly called for Western allies to give Ukraine permission to fire long-range missiles at targets inside Russia, which is a crucial element to the Ukrainian president’s plan to end the war.

Russia has expanded the use of so-called glide bombs this week to strike the southern Ukrainian city of Zaporizhzhia. At least three glide bombs also hit a central park Kramatorsk in Ukraine’s Donbas region on Wednesday, killing two people.

Ukraine has developed its own long-range drone programme that has been hitting Russian targets but these weapons have not been powerful or accurate enough to strike Russia’s most dangerous military bases.