Tennis authorities denied they were suppressing evidence of match-fixing amid reports on the opening day of the Australian Open alleging widespread corruption at the top level of the sport.

In the reports published before the tournament began Monday, the BBC and BuzzFeed News alleged that the Tennis Integrity Unit, the sport's anti-corruption body, had failed to thoroughly investigate a core group of 16 players that bookmakers, foreign police and other investigators had warned it about, which included winners of singles and doubles Grand Slam tournaments.

The reports said that none of the players had faced any sanctions and more than half would be playing at this year's Australian Open. The players weren't identified by name.

At a hastily convened news conference at the tournament on Monday, ATP chairman Chris Kermode rejected the assertion that match-fixing had gone unchecked, saying the TIU remained "constantly vigilant and not complacent" when it comes to tackling corruption in the sport.

"All of us here in tennis are absolutely committed to stamp out any form of corrupt conduct in our sport," he said. "There is a zero tolerance policy on this."

The BBC and BuzzFeed allegations were based on files they reported had been leaked "from inside the sport" showing evidence of suspected match-fixing orchestrated by gambling syndicates in Russia and Italy that had been uncovered during an ATP investigation of a 2007 match in Poland involving suspiciously high levels of betting.

According to the reports, the ATP investigation widened to uncover a network of other players suspected of match-fixing, but tennis officials didn't follow up on the allegations. Since then, the reports said, the ATP has repeatedly been warned about many of the same players, including a core group of 16 suspected match-fixers, but hasn't taken any action against them.

Novak Djokovic, after opening defence of the Australian Open title with a 6-3, 6-2, 6-4 win over Chung Hyeon of South Korea, faced a grilling over the reports.

The allegations, he said, related to matches from almost 10 years ago and didn't involve active players.

"I don't think the shadow is cast over our sport," he said. "People are talking about names, guessing who these players are, guessing those names. But there's no real proof or evidence yet of any active players. As long as it's like that, it's just speculation.

"From my knowledge and information about, you know, the match-fixing or anything similar, there is nothing happening on the top level."

He said he couldn't give a definitive defense of lower-tier tournaments, but added "there is an organization, authorities, people who take care of that on a daily basis and make sure to track it down."

Integrity unit formed in 2008

On Monday, Kermode countered that the integrity unit had been formed in 2008 following the investigation into the suspicious match in Poland as a joint initiative of the International Tennis Federation, the ATP, the WTA and the Grand Slam Board to combat match-fixing. Investigations by the unit have since resulted in 18 convictions, including six with lifetime bans, he said.

"The Tennis Integrity Unit and tennis authorities absolutely reject any suggestion that evidence of match fixing has been suppressed for any reason or isn't being thoroughly investigated," he said.

With regards to the allegations that tennis officials have overlooked warnings about players since the 2008 investigation, Kermode maintained that the TIU investigates every report it receives and takes action only when it has enough evidence to do so.

"It's about obtaining evidence," he said. "You can have, you know, lots of information, lots of anecdotal reports, but it's about getting evidence that we can use."

Nigel Willerton, head of the TIU, echoed Kermode's statement, saying that "everything that comes into the unit is actioned, it's assessed."

"But as I say, corruption is very difficult to detect and to obtain the evidence to prosecute these people who unfortunately go down that path," he said.

Willerton declined to say whether any players were being monitored at the Australian Open for suspected match fixing.

"It would be inappropriate for me to make comment as to whether any players are under investigation at the present time," he said.