ST PETERSBURG, Russia (Reuters) - Russian President Vladimir Putin said on Wednesday that the West was wrong to assume that Moscow would never use nuclear weapons and said that he was considering deploying conventional missiles in striking distance of the United States and its allies.

Russia's full-scale invasion of Ukraine in 2022 touched off the worst breakdown in relations between Russia and the West since the 1962 Cuban Missile Crisis - and the Kremlin has repeatedly warned that the risk of a global war is rising.

Putin, speaking face-to-face to senior editors of international news agencies for the first time since the war in Ukraine began, dismissed Western claims that Russia could attack NATO as "stupid", citing the military strength of the alliance.

But when asked about the risk of nuclear war, the 71-year-old Kremlin chief said that Russia's nuclear doctrine did allow the use of such weapons if the country's territorial integrity or sovereignty was threatened.

"For some reason, the West believes that Russia will never use it," Putin said when asked by Reuters about the risk of nuclear escalation over Ukraine during more than three hours of questioning.

"We have a nuclear doctrine, look what it says. If someone's actions threaten our sovereignty and territorial integrity, we consider it possible for us to use all means at our disposal. This should not be taken lightly, superficially."

Russia's published 2020 nuclear doctrine sets out the conditions under which a Russian president would consider using a nuclear weapon: broadly as a response to an attack using nuclear or other weapons of mass destruction, or to the use of conventional weapons against Russia "when the very existence of the state is put under threat."

Putin dismissed Western assertions that Russia has employed nuclear sabre rattling and pointed out that the United States was the only country to have used nuclear weapons in war - attacking the Japanese cities of Hiroshima and Nagasaki in 1945.

MISSILES

Putin warned that Western decisions to allow Ukraine to use ever more powerful Western missiles to strike into Russian territory was a serious escalation, and said that such weapons would have to be guided by Western systems and personnel.

President Joe Biden authorized Kyiv to launch U.S.-supplied weapons at military targets inside Russia, but Washington still prohibits Kyiv from striking Russia with ATACMS, which have a range of up to 186 miles (300 km), and other long-range U.S.-supplied weapons.

Asked about the Western decisions, Putin differentiated between different weapons but said that the use of ATACMS or British Storm Shadow missiles against Russia could lead to a tougher response from Moscow.

"We will improve our air defence systems and destroy them," Putin said.

"Secondly, we are thinking that if someone thinks it possible to send such weapons to a war zone to strike our territory and create problems for us, then why do we not have the right to send our weapons of the same class to those regions of the world where strikes can be made on sensitive facilities of the countries that do this against Russia. That is to say, the response can be asymmetric."

"If we see that these countries are being drawn into a war against the Russian Federation, then we reserve the right to act in the same way. In general, this is a path to very serious problems."

Putin casts the war as part of an existential battle with a declining and decadent West which he says humiliated Russia after the Berlin Wall fell in 1989 by encroaching on what he considers Moscow's sphere of influence, including Ukraine.

Putin said the West refused to speak about the causes of the war - which he said started in 2014 after a pro-Russian president was toppled in Ukraine's Maidan Revolution. Putin cast it as a coup backed by the United States.

The West dismisses Putin's analysis of the conflict, and casts the invasion as an imperial-style land grab and has vowed to help Ukraine defeat Russian forces.

Ukraine says it will not rest until every last Russian soldier is ejected from the areas of Ukraine they control - and which Russia now considers to be parts of Russia.

More than two years into the deadliest land war in Europe since World War Two, Russia's leader is increasingly talking of the risk of a global war as the West grapples with what to do about the advance of Russian troops in Ukraine.

Western leaders and Ukraine have played down Russia's warnings about the risk of a broader war involving Russia, the world's biggest nuclear power, but have repeatedly warned that Putin might attack a member of NATO, the world's most powerful military alliance led by the United States.

Both Putin and Biden have said that a direct conflict between Russia and NATO would be a step towards World War Three.

"You should not make Russia out to be the enemy. You're only hurting yourself with this, you know?" Putin said.

"They thought that Russia wanted to attack NATO. Have you gone completely crazy? That is as thick as this table. Who came up with this? It is just complete nonsense, you know? Total rubbish."

(Additional reporting by Vladimir Soldatkin; Editing by Andrew Osborn)

By Samia Nakhoul and Guy Faulconbridge