French Budget Minister Jerome Cahuzac will be under investigation over allegations that he had an undisclosed bank account in Switzerland, the Paris prosecutor's office said Tuesday.

"The Paris prosecutor has as a result decided to open a preliminary investigation for tax fraud," the office said in a statement.

This preliminary investigation comes after the Mediapart investigative website reported that Cahuzac had an undeclared UBS account in Geneva which he then moved to Singapore in 2010. The allegation has been denied by the minister.

The prosecutor's office said that given the sensitivity of the allegations and the time it would take to investigate them, it had no option but to open an inquiry immediately.

The budget minister, who is in charge of battling tax evasion, has filed legal complaints against the website, saying the revealed telephone recording in 2000 that mentioned an account at UBS is not his voice.