French finance prosecutors have asked for Swiss bank UBS to face trial for allegedly orchestrating a vast system of tax fraud in France, a legal source said Monday.

The prosecution requested that UBS face trial for "aggravated laundering of tax fraud proceeds" while its French branch be judged for complicity in these crimes.

It also requested a trial against Raoul Weil, the former head of the bank's global wealth management business, who was charged with tax evasion and illegally canvassing French customers last year, and three other top-level employees.

Investigative judges will now rule on whether the trial will go ahead.

France opened a probe into UBS after former employees blew the whistle over the bank's alleged system of setting up dual accounts to hide the movement of capital into Switzerland between 2004 and 2012.

The banks employees allegedly approached French clients, from wealthy businessmen to sports stars, during receptions, golf tournaments or concerts, to convince them to hide their money in Switzerland.

UBS is accused of using a double accounting method to hide the movement of illicit funds between the two countries.

UBS denies the accusations, arguing that its involvement in such financial operations has not been proven.

Germany last year handed documents to the French judges which allowed them to evaluate the assets of French clients held by the bank in 2008 at nearly 12 billion euros ($13.5 billion), said a source close to the investigation.

However not all involved tax evasion.

The documents also boosted suspicions that the managers of UBS were allegedly aware that a part of these assets were linked to tax evasion.

UBS was first charged with illicit dealings in 2013 and in 2014 with aggravated laundering of tax fraud proceeds.

French judges ordered UBS to pay a record bail of 1.1 billion euros. 

UBS has also been charged in Belgium for tax fraud and featured among the banks which set up offshore companies that were exposed in a vast leak of documents dubbed the Panama Papers.