A dispute between Ankara and The Hague over a rally in support of a Turkish referendum grew on Saturday after a plane carrying Turkey’s foreign minister was barred from landing in the Netherlands, drawing a warning by Turkish President Recep Tayyip Erdogan.

Dutch Prime Minister Mark Rutte said the plane of Turkish FM Mevlut Cavusoglu was barred from landing because his visit would be a threat to public order.

Earlier, Cavusoglu defiantly said he would attend the rally in the city of Rotterdam to drum up support for the April referendum aimed at boosting Erdogan’s powers.

“I am going to Rotterdam today (Saturday),” he told CNN-Turk television in an interview before boarding the plane. “We will impose heavy sanctions on the Netherlands” if the visit is blocked, he added.

Cavusoglu, reflecting growing tensions between Turkey and European allies, said deals with the European Union, including an agreement on stemming a flow of migrants, would be jeopardized if the bloc failed to implement promised visa liberalization for Turks.

He said Turkey would present a final text to the bloc on progress of the deal “and either it will all be cancelled, including the visa liberalization and migrant deal, or it will all be implemented.”

Turkey and the EU last year agreed a deal to stem a record flow of migrants to Europe in exchange for billions of euros in aid to Turkey and the lifting of short-term visa requirements on Turkish citizens.

Rutte said in a statement published on his official Facebook page that Turkey had upset discussions under which Cavusoglu would have been allowed to enter the country, by calling for a massive public rally.

A Turkish threat of sanctions if Cavusoglu were denied entry “made a reasonable solution impossible”, Rutte said.

After the Dutch government withdrew landing rights for Cavusoglu’s flight, Erdogan branded the Netherlands “Nazi remnants, fascists.”

“Ban our foreign minister from flying however much you like, but from now on let’s see how your flights will land in Turkey,” the Turkish president told an Istanbul rally.

Turkish politicians are keen to harness votes of the Turkish community in Europe ahead of the April 16 referendum on whether to boost Erdogan’s powers.

Erdogan accused the Netherlands of working against the “Yes” campaign and said: “Pressure however much you like. Abet terrorists in your country however much you like.

“It will backlash, and there’s no doubt that we’ll start retaliating after April 16… We are patient. Whoever is patient will reach victory.”