Europe's largest under-construction mosque in the French city of Strasbourg received a letter including death threats and insults, a report said Thursday.

Eyüp Sultan Mosque, which is currently being constructed by the Milli Görüş Islamic Confederation (CIMG), received the letter Wednesday.

The anonymous letter, titled "Declaration of War," claimed that there is no space for Islam in France and that Muslims living in the country need to choose between their religion or France.

"Of course, a majority of your congregation would choose Islam. Then why are you still in France?" the letter said.

The letter also told Muslims to be prepared for "unprecedented attacks" against mosques in the country, claiming that their crowd is quite large.

"Prepare well, revenge starts," the letter said.

Eyüp Şahin, the CIMG's chairperson in East France, told Anadolu Agency (AA) that they had previously received such threats, and there has been a surge in threats against Muslims and mosques in Europe.

He noted that he previously received threats saying that their addresses were compromised and that the perpetrators threatened to come out and kill their families, bomb mosques and more.

"Such threats take place Europe-wide. All Muslims receive such threats, but I believe this complex receives more attention because it is the largest of its kind in Europe and the perpetrators want to make their voices heard," Şahin said. He noted that they have informed the police and relevant authorities about the letter, as he said they expect statements with common sense from politicians, rather than provocative remarks that trigger such hatred.

The mosque, located in eastern France, will allow thousands of Muslims living in nearby German and Swiss cities to come and worship and is expected to be finished by year-end. It will have a capacity to hold 2,500 people indoors and 5,000 indoors and outdoors. There will also be a museum on the history of Muslims in France, as well as a research center, a library, restaurant and others.

Earlier this year, the mosque was vandalized with words, "No to Islam, go back to your village," which were sprayed across the fence on the construction site.