European Commission President Ursula von der Leyen accused Alternative for Germany (AfD) of "betraying" Germany.
AfD has been struggling with a series of scandals ahead of European Parliament elections, AFP reports.
Last month, Alternative for Germany was rocked when a parliamentary aide to its leading candidate for next month's European Parliament elections was arrested on suspicion of spying for China.
The candidate, Maximilian Krach, has previously been implicated in allegations of Russian propaganda.
The behaviour of the AfD "is destructively dishonest", Von der Leyen told a Christian Democratic Union (CDU) congress in Berlin.
The party is "making propaganda for Putin and spying for China ahead of the European elections.
"First the AfD speaks loudly about the people and the homeland, and then the AfD betrays this homeland to the autocrats. They should be ashamed of themselves."
The party's agenda in the European elections would destroy jobs, she said, criticising them for flirting with the idea of Germany leaving the EU.
Von der Leyen, a former German defence minister, is seeking a second term as head of the EU executive in the upcoming elections.
The AfD is among the far-right parties in Europe expected to make gains in the elections.
Last year, the anti-immigration party made a sharp jump in the polls, overtaking Chancellor Olaf Scholz's Social Democrats and coming second to the main opposition CDU.
However, support for the party has dropped after recent scandals.
Krach insists he will remain the party's leading candidate for the EU elections despite the arrest of his running mate.
Previously, Krach and another AfD candidate for the EU parliament, Petr Bystron, were forced to deny allegations that they accepted money to spread pro-Russian positions on a Moscow-funded news website.
In addition to the EU elections, the AfD is expected to make gains in three states in Germany's former communist east when closely watched regional elections are held in September. / BGNES
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