Russian and Belarusian players will not be allowed to compete at Wimbledon this year because of the invasion of Ukraine.
Men's world number two Daniil Medvedev of Russia and women's world number four Aryna Sabalenka of Belarus are the highest-ranked players to be affected.
The players are also banned from any of the UK grass-court tournaments.
The governing bodies of men's and women's professional tennis said the move was "unfair".
Serbia's Novak Djokovic, a six-time men's singles champion at Wimbledon, said he did not support the "crazy" decision by the All England Lawn Tennis Club (AELTC).
The men's body, the ATP, said it could "set a damaging precedent for the game", while the women's body, the WTA, said it was "very disappointed".
In a statement, the ATP said: "Discrimination based on nationality also constitutes a violation of our agreement with Wimbledon that states that player entry is based solely on ATP rankings.
"Any course of action in response to this decision will now be assessed in consultation with our board and member councils."
The WTA said it "will be evaluating its next steps and what actions may be taken regarding these decisions".
Djokovic, the men's world number one, added: "The players, the tennis players, the athletes have nothing to do with war. When politics interferes with sport, the result is not good."
Martina Navratilova, who won a record nine Wimbledon singles titles, said excluding Russian and Belarusian players was "not the way to go".
"I think it's the wrong decision. Tennis is such a democratic sport. It is difficult when you see politics destroy it," said the Czech-born American.
Wimbledon runs from 27 June to 10 July.
Which players will be affected by the ban?
Explaining its decision, the AELTC said it had a responsibility to "limit Russia's global influence through the strongest means possible".
"In the circumstances of such unjustified and unprecedented military aggression, it would be unacceptable for the Russian regime to derive any benefits from the involvement of Russian or Belarusian players," a statement from the AELTC read.
"It is therefore our intention, with deep regret, to decline entries from Russian and Belarusian players to Wimbledon."
Sabalenka reached the semi-finals of last year's tournament, while Medvedev, who has been announced as one of the star draws at the grass-court warm-up event at 's-Hertogenbosch in the Netherlands today, reached the fourth round.
Russian world number 15 Anastasia Pavlyuchenkova - who called for the war to stop earlier this year - and 18th-ranked Victoria Azarenka of Belarus will also miss out.
Russia's Andrey Rublev is eighth in the men's standings, with compatriot Karen Khachanov 26th.
Only players are banned, which means coaches, umpires and physiotherapists can be involved in the tournament.
While the Lawn Tennis Association has banned Russian or Belarusian players from competing in the UK this summer, they will all still be able to play at the French Open, which begins in May.
Players from both countries have been allowed to compete on the tennis tour but not under their national flags.
Which sports have banned Russian athletes?
What has the reaction been from the tennis world, Russia and UK politicians?
The ATP said Russian and Belarusian players would still be allowed to compete at its events under a neutral flag.
"Our sport is proud to operate on the fundamental principles of merit and fairness, where players compete as individuals to earn their place in tournaments based on the ATP rankings," it said.
"We believe that today's unilateral decision by Wimbledon and the LTA to exclude players from Russia and Belarus from this year's British grass-court swing is unfair and has the potential to set a damaging precedent for the game."
The WTA said: "Individual athletes should not be penalized or prevented from competing due to where they are from, or the decisions made by the governments of their countries.
"Discrimination, and the decision to focus such discrimination against athletes competing on their own as individuals, is neither fair nor justified. The WTA will continue to apply its rules to reject discrimination and ensure that all athletes are able to compete at our Tour events should they qualify to do so, a position that until today's announcement has been shared across professional tennis."
Kremlin spokesperson Dmitry Peskov criticised the ban.
"Given that Russia is a strong tennis country and our athletes are among those at the top of the world rankings, the tournament itself would suffer because of this ban," he said.
"It is unacceptable to make the athletes once again hostages of certain political prejudice, intrigues and hostile actions towards our country."
The AELTC, which organises Wimbledon, consulted the government in April about whether to allow players to compete.
"We recognise that this is hard on the individuals affected, and it is with sadness that they will suffer for the actions of the leaders of the Russian regime," AELTC chairman Ian Hewitt said.
"Given the importance of not allowing sport to be used to promote the Russian regime and our broader concerns for public and player (including family) safety, we do not believe it is viable to proceed on any other basis at The Championships."
The AELTC is also working to withdraw TV rights from companies broadcasting in Russia and Belarus.
Although the AELTC statement says the decision could be overturned if "circumstances change materially between now and June", that is considered very unlikely.
A statement from the LTA said it is "important to do all it can to support Ukraine at this time".
"The LTA believes that tennis must join many other areas of sport and public life in sending a clear signal to the Russian and Belarusian states that their actions are the subject of international condemnation," a statement read.
"The continuing participation of Russian and Belarusian nationals at events risks providing a boost to these regimes when there is an unprecedented international effort to isolate them and sanction their actions."
UK sports minister Nigel Huddleston welcomed the "decisive action" by the AELTC and LTA.
"The UK has taken a leading role internationally to make clear President Putin must not be able to use sport to legitimise Russia's barbaric invasion of Ukraine. Whilst the withdrawal of individual athletes is a complex issue that will divide opinion, there is a bigger cause at stake."
Culture Secretary Nadine Dorries added: "This decision means Putin won't use the most iconic Grand Slam in tennis to try to legitimise the horrors he is inflicting on the Ukrainian people. The right move."
Russia was previously banned from defending its Davis Cup and Billie Jean King Cup team titles after the country's invasion of Ukraine - a military operation supported by Belarus.
The ATP and the WTA have suspended their combined event scheduled to take place in Moscow in October.
The International Tennis Federation (ITF) has also cancelled its events in the country.
'There comes a time when silence is betrayal'
Ukrainian world number 25 Elina Svitolina released a lengthy statement on Wednesday, calling on tennis' governing bodies to take a harsher stance against Russian and Belarusian athletes.
Svitolina has taken a break from the sport to deal with a back problem and the emotional impact the invasion has had on her.
She posted on social media urging the ATP, WTA and ITF to ask Russian and Belarusian players if they supported the war, the military activities in Ukraine or the regimes of Russian and Belarusian presidents Vladimir Putin and Alexander Lukashenko.
"If applicable, we demand to exclude and ban any Russian and Belarusian athletes from competing in any events," she wrote.
"In times of crisis, silence means agreeing with what is happening.
"There comes a time when silence is betrayal, and that time is now."
Olga Savchuk, who captained Ukraine in last week's Billie Jean King Cup tie against the USA, said Russian players should be banned from competing.
"It cannot just be a sanction against 90% of the Russian people and 10% not," Savchuk told the New York Times.
"It has to be even and I think it is collective guilt."
Ukrainian former world number 13 Alexandr Dolgopolov thanked Wimbledon for "stepping up and showing the world an example".
"I believe Russia should be isolated in all possible ways, and the people of Russia have to solve this problem," he told BBC Sport.
Source: BBC
BDST: 1232 HRS, APR 21, 2022
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