The Turkish president has further ratcheted up the rhetoric against the Netherlands in spite of German plans for a verbal ceasefire in the escalating war of words between Turkey and Europe.

In a televised speech on Wednesday Recep Tayyip Erdoğan railed against the Dutch and reiterated his assertion that they were responsible for the slaughter of Bosnians in Srebrenica in 1995.

“They have nothing to do with the civilised world; they have nothing to do with the modern world,” he declared. “The EU is fast going toward drowning in its own fears.”

In a move intended to symbolise their discontent, authorities in Istanbul announced the scrapping of a twin-town scheme between Istanbul and Rotterdam. Turkey’s red meat association even ordered the expulsion of 40 Dutch cows of the Holstein Friesian breed.

“The Dutch Holstein cows have become very common in our country. But this breed is starting to cause serious problems,” Bulent Tunç, the head of the organisation, told the Anadolu news agency. “In future we do not want animal products from Holland. We have our own quality breeds.”

The Turkish president, who is campaigning for a referendum that could significantly widen his powers, has been openly attacking the Netherlands and Germany since the cancellation of campaign events among the Turkish expatriate community in both countries.

His latest comments came just after Germany told Erdoğan it would allow Turkish citizens to cast their votes on German soil in the upcoming constitutional referendum – on condition that his government cut out its abusive broadsides and reveal its campaign plans.

The German foreign ministry informed the Turkish embassy in Berlin on Tuesday that the approximately 1.5 million Turkish citizens based in Germany would be able to have their say on whether to boost Erdoğan’s presidential powers on 16 April via voting stations across the country.

With stations planned in 13 cities – almost twice as many as at the 2015 elections – Germany would become one of 56 countries to allow voting opportunities to the sizeable diaspora of Turkey, which does not permit postal votes.

However, the German foreign ministry stressed it could withdraw the offer if Turkey didn’t become more transparent about how and where it planned to campaign among the Turkish diaspora in Germany, and if it didn’t “stick to German law” while doing so.

Foreign ministry spokesperson Martin Schäfer said abuses such as accusing Germany of “Nazi practices” would constitute a breach of paragraph 90a of the German penal code. “We are prepared to take all necessary and appropriate measures, including the withdrawal of permissions already granted,” he said.

Angela Merkel’s chief of staff had earlier criticised the Turkish president’s choice of language. “Turkey always attaches great importance to the fact that its honour is not violated,” said the CDU politician Peter Altmaier. “Germany also has an honour.”

“We will take a close look at what is responsible and what is not. An entry ban would be a last resort. But we reserve the right to do that.”

Schäfer said the voting station offer was a sign of the German government’s “generosity”, and pointed out that Bulgarian politicians were currently banned from campaigning among the sizeable Bulgarian minority in Turkey before elections on 26 March.

The European Union’s top officials meanwhile defended the Netherlands against Turkish accusations. Donald Tusk, the president of the European council, told the European parliament: “Rotterdam … totally destroyed by the Nazis, which now has a mayor born in Morocco: If any anyone sees fascism in Rotterdam they are completely detached from reality.”

Tusk’s remarks were echoed by the head of the European commission, Jean-Claude Juncker: “This is totally unacceptable and the one who is doing this is taking distance from Europe and not trying to enter the European Union.”

In his TV address on Wednesday, Erdoğan said of the Netherlands: “They are the ones who massacred more than 8,000 Bosnian Muslims in Srebrenica.”

While around 8,000 Muslim men and boys were killed in the Srebrenica massacre in July 1995, the killings were perpetrated by the Bosnian Serb army. It is likely Erdoğan was referring to a Dutch battalion of UN peacekeepers who failed to halt the slaughter.