A far-right Austrian nationalist has been banned from entering Germany after addressing a meeting about mass deportations that provoked mass protests across the country.

Days after he was deported from Switzerland, Martin Sellner, a leader of Austria’s ethno-nationalist Identitarian Movement, posted a video of himself on X reading out a letter to his lawyer that he said was from authorities in the city of Potsdam.

The letter said Sellner was barred “with immediate effect” from entering Germany for the next three years and could be stopped or deported if he tried to enter the country. If he happened to be on German soil, it added, he would have to leave within a month.

A spokesperson for the city authorities confirmed to Agence France-Presse that an EU citizen had been served with a “ban on their freedom of movement in Germany” but declined to name them for privacy reasons.

“We have to show that the state is not powerless and will use its legitimate means,” Mike Schubert, the mayor of Potsdam, said in a statement.

Germany has seen a wave of huge demonstrations against extremism and the far-right Alternative für Deutschland (AfD) party, some of whose members attended the November meeting in Potsdam, since reports of it emerged in January.

Sellner gave a presentation at the event, attended by neo-Nazis, other extremists and business backers, on the practicalities of carrying out the mass deportations – referred to in far-right circles as “remigration” – of migrants, asylum seekers and German citizens of foreign origin deemed to have failed to integrate.

Swiss police said on Sunday they had prevented a far-right gathering organised by the far-right, anti-Islam and anti-immigration group Junge Tat at which Sellner was due to speak, adding that he had been arrested and deported.

Sellner, who received donations from and communicated with the Christchurch terrorist Brenton Tarrant before the two mass shootings at mosques in 2019 that left 51 people dead, recently had his account on X restored.

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Sellner was banned from Twitter in 2020 under the network’s former management. He praised Musk for restoring his X account last week, where he now has a blue tick associated with paid accounts and 51,000 followers.

“I’m happy and grateful to be back on Twitter/X. I would especially like to thank Musk for making this platform more open again,” Sellner said. “Hope the trend continues and everyone else who has been banned comes back.”

Elon Musk responded to one of Sellner’s posts in which he commented on the Swiss police decision to shut down the weekend far-right event and ban him from the region for two months. The X owner asked: “Is this legal?”