Reports by the BBC and Buzzfeed News say 16 players ranked in the top 50 have been repeatedly flagged to the Tennis Integrity Unit (TIU) over suspicions they had thrown matches in the past decade.

The unit was set up to police illegal activities in the sport.

The reports say it either failed to act on information of suspicious behaviour, or impose any sanctions.

All of the players, including winners of Grand Slam titles, were allowed to continue competing.

Eight of them are playing in the Australian Open, which has just kicked off in Melbourne.

The reports have been rejected by tennis authorities, and couldn't be independently verified by Reuters.

They say an inquiry in 2007 by the Association of Tennis Professionals found syndicates in Russia and Italy making hundreds of thousands of dollars betting on games that investigators believe were fixed.

Three of these games were at Wimbledon.

The BBC and BuzzFeed News say they didn't name players because it wasn't possible to determine if they took part in match-fixing without access to their phone, bank and computer records.