A spokesman for the administrative court in Cologne said the lawsuit and a corresponding emergency petition had been submitted, both of which would be reviewed once the BfV domestic intelligence agency had confirmed that it had been notified.

The extremist classification announced on Friday allows the spy agency to step up monitoring of the AfD, the biggest opposition party in parliament, for example by recruiting informants and intercepting party communications.

The agency’s 1,100-page experts’ report, which is not to be released to the public, found the AfD to be a racist and anti-Muslim organisation.

The German parliament could now attempt to limit or halt public funding for the AfD.

The incoming government will also review whether to launch an attempt at an outright ban of the party, SPD leader Lars Klingbeil said last week.

The AfD has denounced the designation as a politically motivated attempt to discredit and criminalise it.

Its lawsuit comes one day before conservative leader Friedrich Merz is due to be elected chancellor by Germany’s lower house of parliament and amid a heated debate within his party over how to deal with the AfD.