Turkey has upped the ante in its ongoing diplomatic disputes, cutting off all high-level contacts with the Netherlands, even as President Recep Tayyip Erdogan accused German Chancellor Angela Merkel of supporting terrorists.

Tensions between Turkey and other European countries are high after several countries have barred Turkish ministers from rallying expatriate voters in advance of an April 16 constitutional referendum.

The Netherlands has come into particular focus after it blocked visits by two ministers at the weekend.

Turkey responded Monday by closing off its airspace to Dutch diplomats and halting all high-level discussions with the country.

Deputy Prime Minister Numan Kurtulmus said the airspace sanction is effective immediately.

Speaking in Ankara, he added that the Dutch ambassador to Turkey, who is currently on a trip abroad, will not be allowed to return to the country.

Separately, Erdogan accused Merkel of lending support to terrorists.

“Honourable Merkel, you support terrorists,” said Erdogan in a live interview on the A Haber network, in which he also accused German “state television” of backing “terrorist organisations” and trading in propaganda against the presidential system.

He did not cite specifics, but made references to the Kurdistan Workers’ Party (PKK), a group deemed a terrorist organisation by the European Union, but which does get coverage in German media.

Erdogan has lashed out at Merkel and other European leaders several times in the past week, enraged by moves to block Turkish ministers from campaigning abroad for an upcoming referendum that could greatly empower Erdogan.

In a growing war of words, the Turkish president had already labelled the Dutch and German governments fascists and Nazis after planned campaign appearances were banned in those countries.

The ministers are targeting Turkish populations abroad in a bid to boost support for the April 16 referendum on proposed constitutional amendments that would expand the powers of the presidential office.

The Netherlands and Germany are also immersed in election campaigns – the Dutch go to the polls on Wednesday and the Germans later this year – and leaders are eager to show they can take a tough stand against Erdogan as they face a challenge from populist far-right parties.