The French stock market watchdog has launched an investigation into the accounts of troubled media giant Vivendi Universal.

The Commission des Operations de Bourse (COB) said it had sent staff to Vivendi's Paris headquarters to begin examining documents going back to the beginning of last year.

Vivendi, which recently parted company with its flamboyant chief executive, Jean-Marie Messier, has been hit by persistent rumours of accounting irregularities.

Last week, its shares dropped by 40%, after newspaper Le Monde alleged it had tried to add 1.5bn euros to its 2001 accounts as part of a complex transaction involving shares in BSkyB.

News of the investigation came after the Paris exchange closed. Shares in Vivendi had risen 1.7% to close at 18.31 euros

Allegations pile up

A week ago, COB confirmed that it had taken note of the Le Monde story, but said it contained nothing strikingly new.

Such irregularities as may have existed primarily concerned differences between US and French accounting standards, COB said.

It is not yet clear whether the current investigation is based on these or other allegations.

Aside from any accounting concerns, Vivendi has financial troubles that could result in its break-up, analysts say.