A diplomatic row is escalating between Belgium and the US, with Donald Trump’s ambassador refusing to apologise for accusing his host country of antisemitism and reportedly threatening to bar a socialist politician from travelling to the US.

Bill White, a staunch ally of the president like many US ambassadors, on Monday demanded Belgium drop a “ridiculous” and “antisemitic” investigation into three Jewish men suspected of performing circumcisions without medical qualifications.

In a social media post, White demanded Belgium’s “very rude” socialist health minister, Frank Vandenbroucke, stop the “unacceptable harassment” and “disgusting” treatment of the three men. He also called on Belgium to do “a much better job” on antisemitism.

Circumcision is legal in Belgium but must be carried out under strict conditions by a medical professional. The investigation concerns three mohels, or ritual circumcisers, in Antwerp suspected of performing circumcisions without any medical training.

White’s post drew an immediate rebuke from Belgium’s foreign minister, Maxime Prévot. “Any suggestion Belgium is antisemitic is false, offensive, and unacceptable,” Prévot said, accusing the ambassador of violating “fundamental diplomatic norms”.

White responded that Belgium should change its law or label the investigation into “three beautiful religiously qualified and wonderful men” antisemitic. Accusations that he was interfering in Belgium’s judicial affairs were a “political distraction”, he said.

After being summoned to the foreign ministry on Tuesday, White insisted there was “no need” for him to apologise. He had “explained our position and that of President Trump and of our country”, he said, and hoped Belgium could “legalise this process”.

Belgian authorities said White had been reminded of the Vienna convention on diplomatic relations, adding: “Personal attacks on a member of the government and interference in Belgium’s internal affairs are contrary to these basic diplomatic rules.”

The ministry said in its statement that while Belgium attached great importance to its relationship with the US, dialogue “must be based on respect for our institutions and our sovereignty”. It reaffirmed its condemnation of antisemitism and racism.

The Belgian newspaper De Morgen reported on Wednesday that White had handed an official complaint to Belgium’s top diplomat at the meeting, demanding “immediate condemnation” of statements by Conner Rousseau, the leader of the Flemish socialist Vooruit party.

Rousseau last month posted that the “gruesome” behaviour of Immigration and Customs Enforcement (ICE) in the US showed “history was repeating itself” and “we have not listened” to the calls of “never again” after the horrors of Nazi Germany.

Rousseau said on Wednesday he was unrepentant. “I posted that on social media five weeks ago, and yesterday it suddenly turns out to be a problem,” he said. “I suspect [White’s] intervention regarding the circumcision did not go as he would have liked.”

Rousseau, whom White reportedly threatened with a travel ban to the US, told the Flemish broadcaster VRT: “I can only say that we in Belgium have the right, and I also believe a political duty, to express our concerns about what’s happening in the US.

“I respect the ambassador’s opinion, but I also ask for respect for ours.”