The celebrated French philosopher Bernard-Henri Levy has made an impassioned plea to voters to reject "far-right louts" in Sunday's local elections runoffs.

Levy rejected claims that the Front National, which made spectacular gains in the first round of voting last Sunday, had become less extreme under the direction of Marine Le Pen, who has been credited by some with softening the party's policies.

He published what he described as a "sickening" list of alleged background details of more than a dozen FN candidates.

"The idea that the FN might get its hands on French cities and towns concerns me greatly. I am ashamed that in my country, women and men could give the keys of those cities and towns to these people," he said.

"We're not talking abut the past. We're talking about the present. I can accept that people might change with time, but these people have not changed. The FN has not changed. It has undergone a recycling operation. But just as money that is laundered remains dirty, so do these people."

Levy said he and his staff had spent months checking the backgrounds of the FN candidates before publishing the details on his website.

The independent news site Basta published a similar list of FN candidates with allegedly questionable backgrounds at the time of France's general election in 2012, in an article headlined "Welcome to the museum of extreme right horrors".

Ivan du Roy, Basta's editor and the author of that article, agreed that the FN had not changed. "There have been a few new people brought in, but those who are at the heart of the party still represent the extreme right. The spinal column of the FN has not changed," he said.

"Our job is to publish this information because these people are looking to run our cities, and later others seek to be elected to the European parliament. Afterwards, it's for voters to make their choice, and to take responsibility for that choice when they discover they don't like what the people representing them are then doing."

Among those cited by Levy is Thibault de la Tocnaye, an FN candidate at Avignon, who has made no secret of his anti-Islam stance, and who fought with Christian militia in Lebanon in the early 1980s.

Another named is Jean-Pierre Baumann, a candidate in Marseille, who at the trial of three FN activists accused of murdering 17-year-old Ibrahim Ali in 1995 said: "French people of French origin, we know them, they are all white."

Gilbert Collard, a lawyer who represented Ali's friends in the same trial, went on to become Marine Le Pen's spokesperson. Collard later defended an army general convicted of crimes against humanity for torturing prisoners in the Algerian war, saying of his client: "His most noble decoration was the opprobrium."

Levy also lists Laurent Comas, another FN candidate in Marseille, whose campaign director, Pierre-Olivier Sabalot, a former skinhead, was sentenced to two years in jail after dumping a Kalachnikov, a bottle of sodium chlorate and magazines on explosives in a city park in 2002.

Another candidate, Frédéric Boccaletti, was sentenced to a year in prison, six months suspended, for "premeditated gang violence with a weapon" in 2000. He was also arrested for selling "racist" literature.

Levy wrote: "This listing, which could have been much longer – much, much longer – is sickening. And one trembles with anger at the thought of having had to print, here, the names of these people and the details of their infamies.

"Readers of this note who believe, in good faith, in the alleged de-demonisation of the FN, take action, before it is too late. The Front National – and this can be verified in a click by every well-meaning citizen – is not, for the right nor the left, an adversary like any other. The Front National – I say this calmly, sticking to the facts – is not a solution for those who despair of the deleterious climate in which French political life is swamped.

"One can, if one is of the right, beat the left without mercy. One can, if one is of the left, seek to defeat the right. One cannot, if one is a republican, give the keys to our towns and cities to men and women who represent the worst there is."

The FN said no one was available to comment on Levy's remarks.