"I won't say another word about these things," the conservative contender said on French television, condemning "successive revelations, carefully disseminated by state services."
The revelation comes as France gears up for the first balloting in the two-stage presidential race on April 23.
Fillon, once the race's frontrunner and who denies any wrongdoing, was charged with abuse of public funds last month in a scandal that he has blamed on the outgoing Socialist government.
The 63-year-old is accused of giving fake jobs to his Welsh-born wife Penelope that earned her 680,000 euros (AUD$961,000) in salary payments between 1986 and 2013.
Mediapart said late Monday that "Penelope Fillon in fact benefited from public funds from the first parliamentary mandate of her husband through contracts for studies or projects that he commissioned."
Watch: French election campaign offically begins
Fillon, first elected to represent the central Sarthe region in 1981, went on to become prime minister under president Nicolas Sarkozy from 2007 to 2012.
Other accusations of financial impropriety have piled up since the claims first broke in January, including that Fillon failed to declare an interest-free loan and that he accepted gifts of bespoke suits from a wealthy friend.
Fillon has seen his poll numbers decline since the scandal broke to around 17-19 points, neck-and-neck with far-left candidate Jean-Luc Melenchon and behind centrist Emmanuel Macron and far-right leader Marine Le Pen.
German Finance Minister Wolfgang Schaeuble on Tuesday broke with his country's official neutrality on Tuesday by expressing a preference for Macron over Fillon, saying the conservative's response to the scandals had "not been very encouraging".
"Don't put me in a difficult spot, you know who my political family is," Schaeuble told a debate organised by the Spiegel weekly, in reference to his conservative CDU party which is affiliated in Europe with Fillon's Republicans.
But Schaeuble added: "If I was French, if I was able to vote... I would probably vote for Macron."
French presidential election candidates Francois Fillon, Emmanuel Macron, Jean-Luc Melenchon, Marine Le Pen, and Benoit Hamon. Source: AAP
Why now? lawyer asks
Fillon's lawyer Antonin Levy confirmed that investigators seized "contracts for studies" during a raid of the candidate's parliamentary offices in late January but said they were of "no interest" to the probe which he said reaches back only to 1997.
"The real question is why the financial prosecutor, which has known of these documents for weeks, has not spoken of them and why this information is coming out two weeks before the first round," Levy told AFP.
Fillon was the surprise winner of the rightwing Republicans party's November primary after campaigning on his squeaky clean image.
His two leading rivals, Sarkozy and former prime minister Alain Juppe, were both tainted by legal woes.
Fillon has said that incumbent President Francois Hollande, who decided in December not to run for re-election, headed a "secret cabinet" responsible for the explosive fake jobs revelations.
