Mr Kasparov, who is now chairman of the Human Rights Foundation and has stood as an opposition politician in Russia, claimed as soon as the first Russian tank crossed the border of Ukraine, "the West declared Putin the ruler of the largest country in Europe".
He said: “I was called a warmonger in 2014 when I said Putin would not stop with Crimea and East Ukraine. Now everyone admits that I was right, but wants to repeat the same mistake now. Letting Putin destroy Ukraine increases the threat of a greater conflict, including nuclear.”
Former world chess champion Mr Kasparov formed the United Civil Front movement and joined as a member of The Other Russia, a coalition opposing the administration and policies of Mr Putin.
He announced his intentions to stand as a presidential candidate in the 2008 election, but withdrew, blaming "official obstruction". He fled to New York in 2013 out of fear of persecution and now lives in Croatia.
Mr Kasparov said: “This isn't about Nato. There is only fear, the same fear that kept them from acting in 2014 and led us here.
"As soon as the first Russian tank crossed the border of Ukraine, the West declared Putin the ruler of the largest country in Europe. No longer sovereign, no longer allowed to invite allies to fight in its own territory in its defence. Only Putin can do that.”
The chess grand master accused US and European leaders of wanting to “go back to their comfortable corruption, buying Russian oil and gas, applying weak sanctions, lip service about democracy, inviting Putin to summits and Davos”.
He added: “The West loves to lose slowly, to pass the hard choices to the next admin, shift the consequences to buffer states.
"Now Ukraine has exposed them because Ukraine doesn't want to lose slowly or lose at all. Ukraine wants to win. Help them win. Give jets, drones and long-range weapons that allow Ukraine to strike at the source and protect their people. Ukraine is not Putin's. Stop treating it like it is."