The International Tennis Federation (ITF) has acknowledged that Kazakhstan's Kirill Parfenov was banned for life in February 2015, while Croatia's Denis Pitner received a 12-month sanction in August of the same year.

Both were named by The Guardian today and the ITF has been criticised for not releasing details of the bans at the time.

The delay for the news to become public has led to allegations that the umpires were, in effect, sanctioned in secret.

Parfenov received his life ban for speaking to another official on Facebook  in a bid to manipulate the scoring of matches.

Pitner, meanwhile, was banned for sending details about a player's well-being to a coach during a tournament and logging on to a betting account from which bets were placed on tennis matches.

According to The Guardian, the four umpires facing sanctions are accused of taking bribes to manipulate matches on the ITF's Futures Tour.

This allowed gamblers to place wagers already knowing the outcome of points, it is claimed. 

"Kirill Parfenov of Kazakhstan was decertified for life in February 2015 for contacting another official on Facebook in an attempt to manipulate the scoring of matches," an ITF statement said.

"Separately, Denis Pitner of Croatia had his certification suspended on 1 August 2015 for 12 months for sending information on the physical well-being of a player to a coach during a tournament and regularly logging on to a betting account from which bets were placed on tennis matches.

"The decision to sanction both officials under the ITF Code of Conduct was taken following Tennis Integrity Unit (TIU) investigations.

"This approach is being reviewed as part of the recently announced Independent Review of Integrity in Tennis that will be chaired by Adam Lewis QC.

"To ensure accuracy of reporting, four officials are currently suspended pending the completion of ongoing investigations by the TIU.

"In order to ensure no prejudice of any future hearing we cannot publicly disclose the nature or detail of those investigations.

"Should any official be found guilty of an offence, it will be announced publicly."

The news is another blow for tennis after allegations of match-fixing were revealed on the eve of the Australian Open last month.

An investigation by the BBC and Buzzfeed claimed that 16 players, ranked in the top 50 in the world across the past decade, have been repeatedly flagged as having potentially thrown matches.

It was also alleged that the players were allowed to continue playing despite reports being made to the TIU, which is a joint initiative of the Grand Slam Board, the ITF, the ATP World Tour and the Women's Tennis Association (WTA).