The far-right German party Alternative für Deutschland (AfD) has been expelled from its pan-European parliamentary group after a string of recent controversies over its policy choices and the conduct of some of its leaders.

“The bureau of the Identity and Democracy group in the European parliament has decided today to exclude the German delegation, AfD, with immediate effect,” the ID group of populist far-right parties said in a statement on Thursday.

The day before, AfD’s lead candidate in June’s European elections resigned from the party leadership and renounced all further campaign activities following criticism of comments he made last weekend that the Nazi SS were “not all criminals”.

“The ID group no longer wants to be associated with the incidents involving Maximilian Krah, head of the AfD list for the European parliamentary elections,” the group said on its Facebook page.

Sources within the ID group said they had sped up a decision that was due to take place after the European elections after Krah’s controversial interview. It was a majority decision, with votes cast through a written procedure on Thursday, they said.

Krah’s comments to the Italian newspaper La Repubblica prompted France’s far-right National Rally (RN), a key member of ID along with AfD since 2019, to say this week it would no longer sit in the same group as the German party after the elections.

Marine Le Pen, RN’s leader, who has spent years trying to normalise her party to appeal to mainstream voters, announced on Wednesday that it needed to make a “clean break”, accusing AfD of being held hostage by its most radical elements.

ID, which also includes Matteo Salvini’s League in Italy, Austria’s Freedom party (FPÖ), Geert Wilders’ Dutch Freedom party (PVV) and Vlaams Belang in Belgium, is the more radical and anti-EU of the two hard-right groups in the parliament.

It was set to be the big winner of the 6-9 June elections, with polls projecting that it would boost its seat tally from 59 to 85. But the expulsion of AfD’s forecast 16 MEPs will significantly lessen ID’s expected gains and is likely to precipitate a wholesale recomposition of the parliament’s hard-right forces.

However, the more normalised national-conservative ECR group, which includes Giorgia Meloni’s Brothers of Italy, Poland’s Law & Justice (PiS), Spain’s Vox, the Finns and Sweden Democrats, may be wary of welcoming many former ID members.

ID’s announcement came as candidates to become the next European Commission president sparred over alliances with far-right parties in a debate on Thursday.

Ursula von der Leyen, the incumbent who is seeking a second term, said she was ready to work with Meloni, the Italian prime minister. “I have been working very well with Giorgia Meloni in the European Council,” von der Leyen said.

Meloni, she added, was “clearly pro-European” and against the Russian president, Vladimir Putin. The commission chief again refused to rule out working with Meloni’s ECR group, which includes some parties that many experts consider to be far-right.

The Party of European Socialists’ lead candidate, Nicolas Schmit, who is currently Luxembourg’s EU commissioner and reports to von der Leyen, was sharply critical of her stance.

“Mrs von der Leyen, please bring clarity … I wonder what is pro-European for you,” Schmit said. Referring to Meloni’s speech at a recent far-right gathering in Madrid, he said: “I cannot imagine that her idea of Europe is the same thing you have.”

The centrist candidate Sandro Gozi also came under attack. His Renew Europe group will vote on 10 June – the day after the election results – on whether to expel the Dutch liberal VVD party over its decision to enter government with the far-right PVV.

Terry Reintke of the Greens said after the elections was too late. “I know Renew is committed to the European project, so send a very clear signal,” she said. “Say it has consequences when member parties of [Renew] go into coalition with the far right.”

Leading leftwingers on Thursday also rejected all alliances with the far right in a joint appeal shared with the Guardian. “Turbulent times require a clear course and a firm attitude. They do not tolerate vagueness or cowardice,” the appeal said.

Signatories from a dozen EU member states included the French MEP Raphaël Glucksmann, Frans Timmermans, a leading Dutch Labour party (PvdA) member, the Spanish Socialist Iratxe García and the German Social Democrat Katarina Barley.

AfD has shot up the polls to become Germany’s second most popular party this year, but its support has recently dropped by several percentage points amid intense scrutiny of its increasingly radical stance.

The party faced mass street protests earlier this year after senior figures attended a meeting where the deportation of Germans with immigrant backgrounds was discussed, and over allegations that it harbours agents for Russia and China.

Krah’s aide has been charged with spying for China and the MEP is himself being investigated for alleged links to Russia and China, which he denies. Though he has promised not to make any further campaign appearances, he is still a candidate in the poll.

Last week a German court ruled that domestic security services could continue to keep the AfD under surveillance as a potentially extremist party. The party denies all allegations of racism, dismissing criticism as politically motivated.