US Secretary of State Marco Rubio has harshly criticised Germany after its domestic intelligence agency described the far-right Alternative for Germany (AfD) an extremist entity that threatens democracy and called on the country to reverse course on its own domestic matter.

The top US diplomat described the move as "tyranny in disguise" and took aim at the US ally's immigration policies.

"Germany just gave its spy agency new powers to surveil the Opposition. That's not democracy—it's tyranny in disguise," he wrote in a post on X.

"What is truly extremist is not the popular AfD—which took second in the recent election—but rather the establishment's deadly open border immigration policies that the AfD opposes."

"Germany should reverse course," Rubio added.

The tweet by Rubio comes in response to Germany's domestic intelligence agency's finding, based on a 1,100 page expert report, that AfD is "racist" and "anti-Muslim".

The classification of the party as an extremist entity allows authorities to increase their surveillance, including by recruiting confidential informants and intercepting communications.

It is not the first time a high-level Trump administration official has aligned themselves with the far-right party.

Both US Vice-President J.D. Vance and Elon Musk have voiced support for the AfD.

Germany's domestic intelligence agency, the Federal Office for the Protection of the Constitution (BfV), announced on Friday that it has officially classified the far-right Alternative for Germany (AfD) party as a confirmed right-wing extremist organisation at the national level.

The AfD had previously been designated as a "suspicion case" federally, though several of its regional branches had already been classified as right-wing extremist entities.

The BfV said its conclusion was the result of a thorough expert review conducted over nearly three years.

According to German public broadcaster ARD, the BfV's assessment is detailed in a report exceeding 1,000 pages.

The agency concluded that the AfD's prevailing "ethnic-based concept of the people" is incompatible with Germany's liberal democratic basic order.

In response to the decision, AfD co-leaders Alice Weidel and Tino Chrupalla condemned the move as a serious blow to democracy.

In a statement, they said the party would continue to challenge the classification through legal means, describing it as a "democracy-endangering defamation".

The AfD currently enjoys strong support in public opinion polls. It surpassed the conservative CDU/CSU bloc for the first time last month to become the strongest political party in a national survey.

(This report has been published as part of the auto-generated syndicate wire feed. Apart from the headline, no editing has been done in the copy by ABP Live.)