Last updated on .From the section Tennis

Italian prosecutor Roberto di Martino has called for top tennis players to be investigated

More than two dozen top tennis players should be investigated for possible links to betting rings, according to an Italian prosecutor.

Roberto di Martino says their names have appeared in evidence seized from gamblers suspected of fixing matches.

They include two players who have been ranked in the world's top 20.

So far, only Potito Starace and Daniele Bracciali, two Italians, have been investigated and charged but Di Martino says others should be investigated.

He also told the BBC's File on 4 programme and BuzzFeed News that tennis authorities should be doing more with the evidence he has gathered.

"Surely if these foreign players were Italian, they would certainly have been at least questioned," Di Martino said. "They should have provided some explanations."

However the Tennis Integrity Unit (TIU), external-link which is responsible for investigating corruption in the sport, said it "strongly refutes any suggestion made by the public prosecutor that evidence of match-fixing has been ignored".

Listen to Simon Cox's report for File on 4 at 20:00 GMT on Tuesday on Radio 4, or catch up on the BBC iPlayer

Di Martino has been conducting a two-year inquiry into a suspected match-fixing ring involving Italian tennis players and gamblers.

His inquiry has obtained internet chat logs and recordings of phone calls between players and gamblers.

A former top-50 tennis player had an exchange of Skype messages with a gambler offering him a match-fixing deal

He says more than two dozen non-Italian players are mentioned by the gamblers and believes these players should be investigated by the TIU.

He would not reveal the identity of the players mentioned in the seized evidence but he added: "Interestingly, they are not so-called second-tier tennis players, but also players of some importance."

Starace and Bracciali have been accused of conspiring to fix matches between 2007 and 2011 for up to 50,000 euros (£38,800).

They are due to appear in court in May and deny charges of conspiracy to commit sports fraud.

Di Martino claims he has "concrete evidence" about two specific matches in 2009 and 2011 in Barcelona involving Starace.

He suspects there are 30 other matches that may have been corrupted, by a number of players, including at Wimbledon and the French Open.

Paola Cesaroni: "They had to protect some names we think because they were high-ranking players"

The BBC and BuzzFeed News have learned the names of the players contained in Di Martino's investigation files.

A source close to the inquiry said two of these players had been described in an internet chat log between two gamblers as their "horses".

The source told us using this term could mean the players were under the control of the gamblers.

These chat logs were among hundreds of files prosecutors sent to the TIU three months ago.

But Di Martino said TIU investigators had visited him and made it clear they were "exclusively" interested in the Italian players.

"The international aspect seems more problematic than a situation involving a few Italian players," he said.

"It would be possible to identify, possibly hit, many foreign players who definitely are part of this system."

Daniele Bracciali and Potito Starace playing a doubles match in 2014

Di Martino criticised the TIU for failing to act on hundreds of alerts it has received about suspicious betting on tennis matches.

"I do not understand why there was no real initiative by the integrity unit to establish if there was something dirty behind this," he said.

Tennis has been accused of covering up evidence about widespread gambling on matches by players.

In January, tennis authorities launched an inquiry into corruption after the BBC and Buzzfeed News revealed the TIU had failed to act on repeated warnings about 16 top players suspected of being involved in throwing matches.

The TIU said in a statement it was investigating the allegations against Bracciali and Starace and pointed out it had been attempting to access Di Martino's evidence since October 2014, even employing legal counsel to obtain the information.

"All information received from the public prosecutor is being fully and thoroughly assessed, verified and, where appropriate, investigated under the powers of the Tennis Anti-Corruption Program," it added.