A former EU leader on tech has accused Elon Musk of “lying like hell” by claiming the bloc was trying to stop an interview the owner of X had set up with the co-leader of the German far-right party Alternative für Deutschland.

Thierry Breton, who quit as a European commissioner in September, having overseen the passage of ambitious legislation designed to regulate big tech, said Musk had been disingenuous in claiming the EU was trying to censor his discussion with Alice Weidel, due to take place on Thursday evening.

The US billionaire claimed on Wednesday on his social media platform: “First, the EU tried to stop me from having an online conversation with president @realDonaldTrump. Now they want to prevent people from hearing a conversation with Alice Weidel, who might be the next chancellor of Germany. These guys really hate democracy.”

His tweet was a reference to a letter Breton wrote to Musk before a similar chat with Donald Trump in August. In the letter Breton reminded Musk of his obligation under the Digital Services Act (DSA) not to facilitate the “amplification of harmful content”.

After Musk announced he would be interviewing Weidel, whose anti-immigration party is polling at about 19% in the run-up to Germany’s elections next month, Breton sent a similar warning to Weidel through a post on social media, a step which appears to have prompted Musk’s accusations on Wednesday.

In an interview with the Guardian, Breton said: “Now because I sent a letter to Mrs Weidel, he [Musk] is saying the EU want to prevent people from having a conversation. We are twisting information [here].”

Asked if Musk was lying, Breton said: “He is lying like hell. Nobody tried to stop him from having a conversation with Trump, nobody is trying to stop him having one in Germany.”

The Frenchman said he had always had good and constructive face-to-face relations with Musk but that the Tesla chief had mocked and insulted him online. Recently Musk called him “annoying” and, in August, he cited a quip from the US satirical film Tropic Thunder, inviting the then commissioner to “take a big step back and literally, fuck your own face”.

X was approached for comment.

The spat is the latest in a series started by Musk in recent weeks, including hostile attacks on the British prime minister, Keir Starmer, and the German chancellor, Olaf Scholz, that have provoked fury across Europe.

Breton urged leaders to be vocal about the spread of misinformation and hate. “We need leadership, especially these days. Europe is working only if we have a strong leadership,” he said.

X is under investigation by the European Commission under the DSA, partly shaped by Breton. The company has said it is “cooperating with the regulatory process” and remains “focused on creating a safe and inclusive environment for all users on our platform, while protecting freedom of expression”.

Insiders said an adjudication had been expected in autumn 2023 but the commission had needed to give X time to make its legal defence. Some suggested that conclusions would be published shortly.

Breton declined to comment on the investigation, but said he wanted to stress that the DSA had nothing to do with silencing critics or “stopping freedom of speech”, which he said was “cherished” by all democracies in Europe.

“In Europe, freedom of speech is paramount, it is extremely important in all member states for overall democracy, for the courts of justice, it is something untouchable,” he said.

But, he added, it operated within a framework of laws that also banned antisemitic speech, racist hate speech and terrorist apologists, which tech companies were obliged to heed.

“These are forbidden by law in the physical space, in the street, in the media and now also in the digital space,” he said, adding that social media companies, unlike old media, had an unprecedented power to “accelerate and amplify massively” content to audiences, and that with this power came responsibility.