For weeks, Mr Fillon has fought allegations that his wife was paid for years for work she did not do.

Mr Fillon called the investigation "a political assassination" against him.

President Francois Hollande criticised his words, and accused him of attacking France's judicial system.

"Being a presidential candidate doesn't authorise you to cast suspicion on the work of police and judges... or to make extremely serious accusations against the justice system and our institutions more broadly," Mr Hollande said.

Mr Fillon has been summoned to appear before the judge, Serge Tournaire, on 15 March.

The date is just two days before the deadline for candidates to submit their final applications. The first round takes place on 23 April, followed by a second-round run-off on 7 May.