The far-right, anti-immigration Alternative for Germany (AfD) had been under investigation by the BfV agency for several years, and several local chapters of the party had already been classified as right-wing extremist.

The spy agency said it decided to give the entire party the label as there were numerous instances of the AfD trying to “undermine the free, democratic” order in Germany.

The party “aims to exclude certain population groups from equal participation in society”, said the BfV in a statement.

In particular, the AfD does not consider German citizens with a migrant background from countries with large Muslim populations to be “equal members of the German people”, it added.

“This is evident in the large number of ongoing xenophobic, anti-minority, Islamophobic and anti-Muslim statements made by leading party officials,” it said.

The classification gives intelligence services extra powers to monitor the AfD, lowering the barriers for such steps as intercepting telephone calls and using undercover agents.

The party has surged in popularity in recent years by capitalising on growing concern about migration at a time when Europe’s biggest economy has been mired in recession.

It came second in the general election in February, winning more than 20% of the vote, behind the centre-right CDU of Friedrich Merz, who is due to take office at the head of a coalition next week.