Most of the 11 French presidential candidates are sceptical about the 28-nation European Union, amid growing nationalist sentiment around Europe and Britain's pending exit from the bloc.

But Mr Fillon argued that the EU is "indispensable" to ensure peace and prosperity.

He warned that far-right presidential candidate Marine Le Pen's proposals to leave the EU and the euro currency "would be assured chaos, and the explosion of Europe".

He did say the bloc has become too heavily regulated and needs to "recreate itself".

He proposed tougher protection for external borders and tougher EU rules against trade dumping and tax evasion by US or Asian companies.

Conservative Mr Fillon was once the front-runner in the presidential race but corruption allegations have hurt his chances in the two-round election on April 23 and May 7.

Earlier, Mr Fillon threatened legal action over leaks that have deeply damaged his campaign - and that he believes came from President Francois Hollande.

Mr Fillon said he had detailed information about who was behind the leaks about parliamentary jobs he gave his wife Penelope, from Abergavenny in Wales, and children.

He said "when the time comes, I will pursue them" and "those who are at the origin of the affair will not sleep well in the future".

Mr Fillon has been given preliminary charges of embezzlement but denies wrongdoing.

On Thursday he reiterated accusations that the Socialist president was linked to the leaks - accusations Mr Hollande has denied.