If the West allows Ukraine to use long-range missiles to strike Russia, its options Vladimir Putin retaliation could include striking British military targets near Russia or, in the extreme case, even conducting nuclear test in a sign of intent, analysts told Reuters.

Ulrich Kuehn, a weapons expert at the Institute for Peace Research and Security Policy in Hamburg, did not rule out the possibility that Putin would choose to send some kind of nuclear message. For example, to test a nuclear weapon in an attempt to scare the West.

“This would be a dramatic escalation of the conflict,” he said in an interview. “Because the point is, what kind of weapons would Mr. Putin leave behind if the West follows through, other than actually using nukes?”

Russia has not conducted a nuclear weapons test since 1990, a year before the fall of the Soviet Union. A nuclear explosion would mark the beginning of a more dangerous era, Kuehn said, noting that Putin may feel he is being seen as weak in his responses to growing NATO support for Ukraine.

“Nuclear tests would be something new. I wouldn’t rule it out, and it would be in line with Russia’s violation over the past two years of international agreements it has signed over the past decades,” he said.

Gerhard Mangot, a security expert at the University of Innsbruck in Austria, said in an interview that a nuclear message would be possible, but not likely in his view.

“The Russians could do a nuclear test. They have made all the necessary preparations. They could go ahead with a nuclear explosion somewhere in the east of the country just to show they mean it.”

Russia’s UN ambassador Vasily Nebenzia told the UN Security Council on Friday that the NATO “would be directly involved in hostilities against a nuclear power” if it allowed Ukraine to use longer-range weapons against Russia.

“You mustn’t forget that and think about the consequences,” he said.

Russia, the world’s largest nuclear power, is also in the process of revising its nuclear doctrine – the circumstances under which Moscow would use nuclear weapons.

Putin is being pressured by a powerful foreign policy hawk to make it more flexible in order to open the door to a limited nuclear attack on a NATO member country.