Tyson Fury and Oleksandr Usyk will fight in Saudi Arabia for the undisputed heavyweight championship of the world at a date to be decided, organisers said on Friday after contracts were signed.

Britain's Fury is the WBC world champion while Ukrainian Usyk holds the WBA, WBO, IBF and IBO belts. Both men have unbeaten records.

A long-awaited blockbuster unification fight between the two has failed to get over the line in the past, with a previous attempt to meet at London's Wembley Stadium breaking down amid recriminations on both sides.

Now, with the backing and financial muscle of Saudi Arabia, it appears to be on.

Organisers said it would be promoted by Queensbury Promotions, Bob Arum's Top Rank, K2 and Usyk17 at Riyadh's Kingdom Arena.

"You can't run rabbit run anymore Usyk, you're getting it," Fury, 35, wrote on Instagram.

Heavyweight boxing's last undisputed champion was Britain's Lennox Lewis in 1999, before the current four-belt era.

"This is the fight that everyone has wanted to see for some time and now it is finally happening," said Turki Alalshikh, chairman of Saudi Arabia's General Entertainment Authority, in a statement.

"It is the biggest fight in boxing, the world will be watching, and we are so proud to be the hosts for this spectacle as part of the fourth edition of our Riyadh Season celebrations."

Fury is due to fight former UFC heavyweight champion Francis Ngannou in Saudi Arabia on Oct. 28 in a bout with professional boxing rules. That fight marks the start of the Riyadh Season, a winter festival of sporting and cultural events.

The BBC, citing unconfirmed reports, suggested Fury v Usyk could take place on Dec. 23 or in January.

Queensberry's Frank Warren, who promotes Fury, said he was delighted to get the Usyk fight signed off at last.

"This is the biggest fight that could possibly be made in our sport," he said.

"The heavyweights always spark the imagination of the fans, and I have no doubt this will be the biggest boxing event of the century. I look forward to Tyson reclaiming the three belts that he never lost in the ring."

Fury, the self-styled 'Gypsy King', has held the WBC belt since 2020 when he beat American Deontay Wilder and has a professional fight record of 33 wins and one draw.

He defeated Wladimir Klitschko in 2015 for the IBF, WBA and WBO belts but was stripped of the IBF title when he agreed to a rematch with the Ukrainian rather than facing a mandatory challenger.

In 2016 he had his boxing licence suspended hours after he announced he was relinquishing his WBA and WBO titles to focus on his mental health.

"I can't believe that it's happening but it is," said Usyk's promoter Alex Krassyuk.

Usyk, 36, has a record of 21 wins -- 14 by knockout -- and turned professional after winning the heavyweight gold medal at the 2012 London Olympics.

Saudi Arabia also hosted Usyk's title defence against Britain's Anthony Joshua in Jeddah in August 2022.

The country has dismissed accusations of "sportswashing, using sport to improve an image tarnished by human rights abuses.

(Reporting by Rohith Nair in Bengaluru/Alan Baldwin in London Editing by Toby Davis and Christian Radnedge)