Klitschko - whose brother Vitali, also a former world heavyweight champion, is Mayor of Kyiv - called the collaboration: "A stain on the coat of the noble art" in a Twitter post.

A co-operation agreement was signed on November 28 in Mexico City between WBA President Gilberto Jesús Mendoza and Russian businessman Umar Kremlev, President of the IBA, with Mendoza commenting: "Being able to bring the most important entity of professional boxing closer to the most outstanding of amateur boxing is a huge step towards achieving our goals and integrating this great sport."

With the Russian invasion of Ukraine continuing, Klitschko - a former WBA champion, who signed up with the Kyiv Territorial Defence Brigade shortly after the invasion began on February 24 - added:

"Boxing needs more transparency, not more greed.

"The collaboration between WBA and IBA is a stain on the coat of the noble art.

"The decision to reinstate Russian and Belarusian boxers is an indelible moral fault.

"It is no coincidence that the IOC (International Olympic Committee) persists in excluding boxing from the 2028 Olympic Games.

"Boxing needs one big clean-up."

The WBA has offered its reasoning for why Russian boxers will no longer be excluded saying: "The WBA, through its Championships Committee and Ratings Committee, issued a statement in which it decided to reinstate Russian and Belarusian boxers to their place in the rankings.

"The athletes from this country are not soldiers or part of the Government.

"Therefore, they have nothing to do with the war against Ukraine.

"However, it was determined that any fighter who speaks out in favour of the war or is involved in it will be removed immediately."

Speaking in Mexico City, Mendoza, whose One Boxing project has been one of his main pieces of work since he took up his role in 2015 said: "This agreement with IBA is something that will bring many benefits to boxing.

"I have always had the slogan that Boxing is One and being able to bring the most important entity of professional boxing closer to the most outstanding of amateur boxing is a huge step towards achieving our goals and integrating this great sport."

Both leaders signed the agreement with 10 key points that seeks to promote amateur boxing and the integration of both branches for the systematic development of the sport.

"Within IBA, we are building a global home of boxing," Kremlev said.

"The co-operation between IBA and WBA can provide the future of boxing as a sport.

"Our goal is to build the bridge between the two organisations and give more opportunities to all boxers worldwide."

The IBA is seeking to regain responsibility for boxing at the Olympics, something that was taken out of the hands of its former incarnation, the AIBA, in 2019, with the Tokyo 2020 competition being undertaken by an IOC Boxing Task Force which is set to perform the same function at the Paris 2024 Olympics.

Boxing is not on the provisional programme for Los Angeles 2028, but there is what the IOC has termed a "pathway" for its reinstatement.

insidethegames has asked the IBA for its comment on Klitschko's statement.