Islamists are infiltrating France’s republican institutions and are a threat to national cohesion, according to a report presented to President Emmanuel Macron on Wednesday.

The report, drawn up by two senior civil servants, claims to find evidence for a policy of “entryism” by the Muslim Brotherhood into public bodies like schools and local government.

After a meeting of his security cabinet, Macron asked the government to come up with “new proposals” by early next month in light of the seriousness of the report’s conclusions.

Secularism is a core tenet of France’s national identity.

According to an Élysée official speaking off the record, there is a “new phenomenon – entryism – which is different from separatism”.

While separatism implied Muslims living in a parallel society in France, “entryism means getting involved in republican infrastructure… in order to change it from the inside. It requires dissimulation… and it works from the bottom up,” the official said.

In a copy of the report published in Le Figaro newspaper, the authors identified the Federation of Muslims of France (FMF) as the main French emanation of the historic Muslim Brotherhood, which was founded 100 years ago to promote a return to core Islamic values.

They said the FMF controlled 139 places of worship in France, with a further 68 affiliated – in all around 7% of the total. The organisation also ran some 280 associations, in sports, education, charity and other fields, as well as 21 schools.

The aim of the movement was to set up “ecosystems at local level” to “structure the lives of Muslims from birth till death”.

“[The movement’s] officials, who are hardened activists, enter into a relationship with the local authority… Social norms – the veil, beards, dress, fasting – are gradually imposed as the ecosystem solidifies,” the authors write.

“What happens is that religious practice become stricter, with a high level of girls wearing the abaya (long robe) and a massive and visible increase in the number of young girls wearing Islamic headscarves. Some are as young as five or six.”

The Federation angrily rejected “any allegation that associates us with a foreign political programme, or with a strategy of ‘entryism'”.

“Confusing Islam with political Islamism and radicality is not only dangerous, but counter-productive for the Republic itself,” the FMF said. “Behind these unfounded accusations there is a plan to stigmatise Islam and Muslims.”

The report has been seized on by proponents of a strict enforcement of France’s secular laws, which are meant to exclude all religion from public life.

Interior minister Bruno Retailleau, who on Sunday was elected leader of the conservative Les Républicains party, warned on Tuesday of “below-the-radar Islamism trying to infiltrate institutions, whose ultimate aim is to tip the whole of French society under sharia law”.

Municipal elections are due in France next year, and Retailleau – who has won a reputation as a hardliner – has said he is concerned about the possibility of Islamic lists of candidates.

Far-left leader Jean-Luc Mélenchon warned that “Islamophobia has crossed a line”, accusing the president’s security cabinet of adopting the “delusional theories” of both Retailleau and far-right National Rally leader Marine Le Pen.

The report’s authors, who visited 10 different regions of France and four other European countries, concluded that the Muslim Brotherhood was losing influence in the Middle East and North Africa, and so was targeting Europe, backed by money from Turkey and Qatar.

“Having given a Western look to the ideology in order to implant themselves in Europe, (the Muslim Brotherhood) tries to lay down the roots of a Middle Eastern tradition while concealing a subversive fundamentalism,” they wrote.