Eyup Sahin is pondering how his plans to build a centre of worship in the French city of Strasbourg became such a flashpoint.

In her office a few miles away, city mayor Jeanne Barseghian is reflecting how her life has been turned upside down since the local authority accepted a request from Sahin and his Turkish Islamic organisation for a €2.5m subsidy to build what would be one of Europe’s largest mosques.

The answer, they say, is politics — in particular the campaigning under way between President Emmanuel Macron and far-right leader Marine Le Pen ahead of elections next year. Both are eager to show how tough they are on Islamists, illegal immigrants and Turkey’s president Recep Tayyip Erdogan.

“We were surprised by the intensity of it all,” said the bearded Sahin, as construction of the €32m complex in an old warehouse district continues with the help of donations from worshippers linked to the Milli Gorus (National Vision) Turkish diaspora organisation of which he is the regional head. “It’s political persecution. In elections, people get used, and today we’re the target.”

The controversy erupted last month after Gérald Darmanin, Macron’s hard-hitting interior minister, accused Barseghian — from the opposition green party Europe Ecologie Les Verts — of financing a mosque being built by an organisation that “supports political Islam”.

In January, Milli Gorus, along with three other groups, had refused to sign the “Charter for the Principles of French Islam” being promoted by the Macron government as part of its drive against extremism and Islamist “separatism”.

The charter asserts the compatibility of Islam with the values of the French republic, rejecting political Islam, denying the notion of apostasy and championing gender equality. Sahin said Milli Gorus had not signed it only because its representatives were not consulted and it did not agree with the wording.

Barseghian, attacked by the right as an Islamist sympathiser and by Armenians for supporting the Turkish project despite her Armenian heritage, said she was “shocked” by Darmanin’s accusation, which sparked threats and hate mail.

“The government clearly wants to criticise and attack the greens” ahead of the polls, she said. “[But] it’s a very dangerous game to go for us on subjects such as secularism, republican principles and religion. It divides the country and gives a boost to extremists.”

Darmanin then said he had ordered a legal challenge to the planned subsidy, while government spokesman Gabriel Attal went as far as saying that Milli Gorus, whose western European presence is centred on Germany, had “no reason to organise activities or to exist in France”.

Strasbourg city mayor Jeanne Barseghian

Hombeline du Parc, a local politician for Le Pen’s Rassemblement National party, was also harshly critical of the mayor and said Milli Gorus, which was founded in 1969, was beholden to Erdogan. “People can practise their religion, we’ve no problem with that,” she said. “But foreign interference is unacceptable.”

Samim Akgonul, head of the Turkish studies department at Strasbourg university, said the issue was a political gift for Darmanin as he sought to punish Milli Gorus for refusing to toe the line.

“The French interior minister was searching for revenge, and he found it in Strasbourg over the financing of the mosque,” he said. “Technically speaking the decision [to fund it] was correct. Politically speaking it was a very clumsy move.”

The mosque project, which would serve the 30,000 or so people of Turkish origin in Strasbourg, was approved in 2013, and the first stone was laid in 2017 in the presence of senior French officials and Turkey’s deputy prime minister.

Unlike in the rest of France, where strict secular rules dating back to 1905 ban public funding of new religious buildings, state subsidies are allowed for Catholic, Protestant and Jewish places of worship in Alsace and Moselle because they were part of Germany at the time. Strasbourg, capital of the eastern region, later extended the exemption to Islam, orthodox Christianity, Buddhism and others.

In an open letter to the people of Strasbourg addressing the row, Barseghian said the city had spent more than €22m on subsidies for places of worship since 2008, including €3.7m for mosques. “I deeply regret that our city and its inhabitants have suffered the consequences of these polemics that have stirred up fear, hatred and resentment,” she wrote.

Sahin, whose father emigrated from Turkey to work at the Peugeot plant in the city of Mulhouse and who recalls that Muslims there used to borrow a church for Friday prayers, was philosophical about the project he has championed.

He said the idea of a mosque that could hold 2,500 worshippers was to emulate Strasbourg’s other great religious buildings, including its Roman Catholic cathedral. “We said, why not do something similar, so that Muslim culture and Alsace culture can be married?”

He and two senior Milli Gorus officials visiting from Germany agreed the organisation was religiously conservative but denied that anyone affiliated with it had ever committed a terrorist act.

“What concerns us is that when everything is fine, we’re a French organisation,” he said. “But when there’s a problem, they talk about our origins . . . On the one hand they demand integration — even if we already integrated — but when something goes wrong concerning Islam, they say ‘You’re Turks’. Yet I even have an Alsace accent.”

Milli Gorus has now withdrawn its request for a subsidy and launched a new fundraising campaign. “We wanted to finish it in 2022 or 2023,” said Sahin. “But I think it will now take until 2024 or 2025.”