Brussels - A Belgian inquiry into match-fixing in tennis is investigating "100 individuals", many of them players and coaches, a spokesman for the Belgian Federal Prosecutor's Office said on Friday.

The case involves "a highly structured gang from Eastern Europe, which acts from Belgium and specialises in tennis matches," said Eric Van Duyse, the spokesman.

"They focused on low-stakes games, where it's easier to bribe and cheat," he added.

Van Duyse said the inquiry has spread across seven countries: Bulgaria, Slovakia, Germany, the Netherlands, France, the United States and Belgium.

Four French players were arrested last week, two as they were preparing to play doubles in a third-tier Futures event in Bressuire, in central France, a tournament which carried a total prize fund of $15,000.

The four players were released on Wednesday, but are still being investigated. They are suspected of taking bribes to help fix matches at Futures and second-tier Challengers events.

"These are players who have come close to an ATP pro career but who today are struggling to make ends meet," a French police source told AFP.

"The bribes go up to 3,000 euros," said the police source, adding that at a lesser tournament, even winning the title often nets only 2,000 euros.

In Belgium, six members of the suspected network at the heart of the conspiracy have been charged. The