The politician and staunch critic of the Russian President denounced Putin and those who supported, appeased or ignored his activities on Twitter.

"Every dollar in trade with Russia since he invaded Ukraine in 2014, every Euro of corrupt deals with his cronies, helped Putin build the war machine he is using to slaughter civilians in Europe today," Kasparov said after the military operation was launched.

"Now you must help Ukraine fight against the monster you helped create.

"There's no going back in time, but I hope those who ignored, downplayed, and appeased Putin for so long feel some shame today.

"Enough at least to do everything possible to stop him now."

United Nations General Antonio Guterres told Putin to "stop your troops from attacking Ukraine" at an emergency meeting of the UN Security Council in New York.

It was during this session the military invasion began.

Former boxer Wladimir Klitschko, who joined the Ukrainian reserve army three weeks ago, posted his support for his nation on Twitter.

"Be sure: Ukraine is strong," the former Olympic gold medallist and world heavyweight champion tweeted.

"It has a strong capital #Kyiv, strong cities, villages and a strong solid and united people who value above all their independence, sovereignty and peace in Europe.

"Its WILL to exist is infinite.

"Glory to Ukraine!"

Wladimir’s brother Vitali, also a former world champion, is the mayor of Kyiv.

Today he declared an emergency in the Ukrainian capital and is now under martial law.

The Klitschko brothers later published a joint video in Ukrainian, Russian and English appealing for unity.

"I’m calling to all international partners to observe this tragedy that is happening nowadays in Ukraine," Wladimir said in the English edition.

"And this senseless war that is not going to have any winners, but losers.

"I just want to tell you we must stay united against this aggression, against Russian aggression.

"Don’t let it continue happening in Ukraine, don’t let it happen in Europe and eventually in the world.

"United we are strong, support Ukraine, thank you."

Ukrainian Manchester City defender Oleksandr Zinchenko originally posted an Instagram story of Putin wishing he die a "painful suffering death" and called him a "creature".

The post was deleted, and Zinchenko alleges Instagram took the post down.

Two days ago, the footballer released a statement on the platform where he said his "country belongs to Ukrainians and no one will ever be able to appropriate it".

Compatriot and fellow football Andriy Yarmolenko also published his support for his country.

"I call on every Ukrainian to unite, to show his loyalty to the country, to support our army," he said.

"Our strength is freedom, the right to choose, respect and human values.

"Our choice is European Ukraine.

"We are a strong nation, we are on our land and the truth is behind us!"