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EXPLAINER-Might Russia use nuclear weapons in the Ukraine war?

By Arshad Mohammed and Robin Emmott

May 6 (Reuters) - At the start of Russia's invasion of Ukraine, Russian President Vladimir Putin obliquely raised the possibility of a nuclear strike against anyone who intervened in the conflict.

Below are some of the key issues surrounding the possibility - viewed as remote by many analysts and Western diplomats - that Putin might actually use nuclear weapons.

WHAT HAS RUSSIA SAID ABOUT NUCLEAR ARMS IN THE UKRAINE WAR?

In a speech announcing the invasion of Ukraine on Feb. 24, Putin gave a veiled but unmistakable warning that if the West intervened in what he has called a "special military operation" he could use nuclear weapons in response.

"No matter who tries to stand in our way or ... create threats for our country and our people, they must know that Russia will respond immediately, and the consequences will be such as you have never seen in your entire history," he said according to a Kremlin translation.

Three days later on Feb. 27, Putin ordered his military command to put Russia's nuclear deterrent forces on high alert, citing what he called aggressive statements by NATO leaders and Western economic sanctions against Moscow.

Russian Foreign Minister Sergei Lavrov, a veteran diplomat, has also talked about the risk of nuclear war, though he said Moscow was doing its utmost to prevent one.

"I would not want to elevate those risks artificially. Many would like that. The danger is serious, real. And we must not underestimate it," he said last week, prompting the U.S. State Department to call his remarks "the height of irresponsibility".

While Washington has not seen any actions suggesting Russian nuclear forces are on high alert, experts and Western officials warned against dismissing the comments as bluster given the risk Putin could use nuclear arms if he felt cornered in Ukraine or if NATO entered the war.

WHAT HAS THE WEST SAID ABOUT PUTIN'S VEILED THREATS?

U.S. officials quickly called Putin's comments about putting Russian nuclear forces on high alert dangerous, escalatory and totally unacceptable, while NATO Secretary General Jens Stoltenberg criticized them as aggressive and irresponsible.

However, U.S. officials also immediately made clear they had seen no signs Russian forces had changed their nuclear posture and the U.S. military said it saw no need to alter its own.

On Feb. 28, U.S. President Joe Biden told Americans not to worry about a nuclear war with Russia. Responding to a shouted question about whether U.S. citizens should be concerned about a nuclear war erupting, Biden said "no."