LONDON (Reuters) - Vladimir Putin's options to retaliate if the West lets Ukraine use its long-range missiles to strike Russia could include striking British military assets near Russia or, in extremis, conducting a nuclear test to show intent, three analysts said.
As East-West tensions over Ukraine enter a new and dangerous phase, British Prime Minister Keir Starmer and U.S. President Joe Biden are holding talks in Washington on Friday on whether to allow Kyiv to use long-range U.S. ATACMS or British Storm Shadow missiles against targets in Russia.
President Putin, in his clearest warning yet, said on Thursday that the West would be directly fighting Russia if it went ahead with such a move, which he said would alter the nature of the conflict.
He promised an "appropriate" response but did not say what it would entail. In June, however, he spoke of the option of arming the West's enemies with Russian weapons to strike Western targets abroad, and of deploying conventional missiles within striking distance of the United States and its European allies.
Ulrich Kuehn, an arms expert at the Institute for Peace Research and Security Policy in Hamburg, said he did not rule out Putin choosing to send some kind of nuclear message - for example testing a nuclear weapon in an effort to cow the West.
"This would be a dramatic escalation of the conflict," he said in an interview. "Because the point is, what kind of arrows has Mr Putin then left to shoot if the West then still continues, apart from actual nuclear use?"
Russia has not conducted a nuclear weapons test since 1990, the year before the fall of the Soviet Union, and a nuclear explosion would signal the start of a more dangerous era, Kuehn said, cautioning that Putin may feel he is seen as weak in his responses to increasing NATO support for Ukraine.
"Nuclear testing would be new. I would not exclude that, and it would be in line with Russia shattering a number of international security arrangements that it has signed up to over the decades during the last couple of years," he said.
Gerhard Mangott, a security specialist at the University of Innsbruck in Austria, said in an interview he also thought it was possible, though in his view not likely, that Russia's response could include some form of nuclear signal.
"The Russians could conduct a nuclear test. They have made all the preparations needed. They could explode a tactical nuclear weapon somewhere in the east of the country just to demonstrate that (they) mean it when they say we will eventually resort to nuclear weapons."
Russia's U.N. ambassador Vassily Nebenzia told the U.N. Security Council on Friday that NATO would "be a direct party to hostilities against a nuclear power," if it allowed Ukraine to use longer range weapons against Russia.
"You shouldn’t forget about this 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 in which Moscow would use nuclear weapons. Putin is being pressed by an influential foreign policy hawk to make it more flexible in order to open the door to conducting a limited nuclear strike on a NATO country.
BRITISH BLOWBACK
In the case of Britain, Moscow was likely to declare that London had gone from a hybrid proxy war with Russia to direct armed aggression if it allows Kyiv to fire Storm Shadow missiles at Russia, former Kremlin adviser Sergei Markov said on social media platform Telegram on Friday.
Russia was likely to close the British embassy in Moscow and its own in London, strike British drones and warplanes close to Russia, for example over the Black Sea, and possibly fire missiles at F-16 warplanes that carry the Storm Shadows at their bases in Romania and Poland, Markov predicted.
Putin has tried and failed to draw red lines for the West before, prompting Ukrainian President Volodymyr Zelenskiy - who is urging the West to be less cautious when it comes to confronting Moscow - to dismiss their importance.
But Putin's latest warning on long-range missiles is being seen inside and outside Russia as something he will have to act on if London or Washington allow their missiles to be used against Russia.
University of Innsbruck's Mangott said the way Putin's warning has been shown repeatedly on Russian state television created an expectation that he would need to deliver.
Dmitry Peskov, Putin's spokesman, told a press briefing on Friday that Putin's message had been "extremely clear and unambiguous."
Markov, the former Kremlin advisor, said "Russia has decided to break" the strategy of "boiling a frog on a slow flame," referring to the West's incremental increases in help to Ukraine aimed at not provoking a sharp Russian response.
"The step that the West is now planning next, it's a small step, but it crosses a red line that we will actually be forced to respond to. We will consider that you are at war with us."
Sergei Mironov, the leader of a pro-Kremlin political party, said in a press statement on Friday: "The moment of truth has come for the West, whether it desires a full-scale war with Russia."
UKRAINE ESCALATION
Short of nuclear sabre rattling or strikes on British assets, more predictable responses might include Russia stepping up attacks on Ukrainian civilian infrastructure, Kuehn said.
Mangott predicted Kyiv would bear the brunt of Russia's military response if the West gave it the requested green light, and he did not expect a Russian military attack on NATO territory.
Another option would be for Russia to escalate "hybrid" actions such as sabotage in Europe or interference in the U.S. election campaign, Kuehn said.
Mangott said the danger for the West was that it did not know where Putin's red lines really were.
"Allowing Ukraine to use Western weaponry, assisted with Western satellite images (and) Western military advisers is something that very closely encroaches on vital Russian interests," he said.
"So I think those (people) are wrong who say 'Well nothing will happen, let's just do it.'"
(This story has been refiled to fix a typo in the headline)