Garry Kasparov, the chess grandmaster and political activist, has accused Western leaders of treating Russia in the same way that former British Prime Minister Neville Chamberlain appeased Nazi Germany.
The former world champion, who in recent years has become a vocal critic of Vladimir Putin and the Russian regime, claimed the West's statesmen have shown weakness in dealing with Moscow by failing to take strong enough action to deter the Russian president and by stating publicly they would not provide military assistance to Ukraine.
Kasparov speculated that Putin did not believe that the sanctions imposed by the West as a result of the Ukraine crisis would last, and warned that the threat of economic ruin could make the Russian president's actions more volatile.
Ukraine's territorial integrity was guaranteed by the UK, USA and Russia in the Budapest Memorandum in exchange for Kiev handing over control of its nuclear arsenal to Moscow.
Kasparov, 51, warned that the consequences of failing to uphold the agreement could lead to nuclear proliferation. He said: "The consequences of this Ukrainian crisis could be felt way beyond Ukraine, the former Soviet Union or Europe. We have to pray that the Western politicians will eventually recognise the dangers. My problem is today you have so many politicians lining up to become a new Chamberlain. Where are the Churchills?"
Kasparov, who was speaking on a visit to the British Houses of Parliament to promote chess being taught in schools, said the Russian president - a former KGB spy - preferred other games.
He said: "Putin does not play chess. Putin plays poker, Putin plays games where he can bluff. Chess is a game with strict rules and open information. As a KGB operative, he prefers to play games where he can trick his opponents by his superior fighting skills. He can bluff with a pair of sixes and his opponents are folding their cards with a full house."
Asked about the West's response to Putin, Kasparov said: "He doesn't believe them. They could be tough in speaking but he still believes that sanctions will not last."
He added: "The problem for me is not that the Western leaders are not willing to impose new sanctions, the problem is they keep showing their weakness. When people ask 'what do you want Western leaders to do first', I can start telling them what they shouldn't do: they should stop telling Putin what they will not do.
"I know that America or the UK are not going to send troops to Ukraine, but why say about it publicly? Why are you saying no boots on the ground? There are many other things 'you are not going to do this', yes, fine. Unlike a normal business negotiation, why are you saying this? If you have got a statement, even if it's obvious, if it's still being said it's a sign of weakness."
Kasparov said the economic difficulties facing Russia could force Putin to adopt a more aggressive foreign policy. "The problem is the regime which is heading for bankruptcy could be even more dangerous. Because you have a dictator who has nothing else but aggressive foreign policy to justify him staying in power for so long.
"Russia today is a one-man dictatorship, which is the most unstable and dangerous form of governance. Unlike the Soviet Union or modern China there is no bureaucratic apparatus that could prevent the leader from making some drastic moves that could endanger the whole system."