Turkey's leaders continued their verbal assault on the Netherlands on Sunday with its foreign minister accusing his NATO ally of being "the capital of fascism".

Foreign Minister Mevlut Cavusoglu made the comments in France where he spoke to whip up support among Turkish immigrants for constitutional reforms to expand the powers of the Turkish presidency.

On Saturday, Cavusoglu was denied landing rights by the Netherlands, where he planned to hold a rally in Rotterdam. Holding political rallies for another country's domestic policies is illegal in Holland.

"The Netherlands - the so-called 'capital of democracy' - and I say this in quotation marks because they are actually the capital of fascism," Cavusoglu said on Sunday in the northeastern French city of Metz.

READ MORE: Turkey-Netherlands row shows no sign of ebbing

Turkish President Recep Tayyip Erdogan said on Sunday at a rally in Istanbul that it was appropriate to accuse the Dutch government of "Nazism and fascism" because "only those types of regimes would bar foreign ministers from travelling within their countries".

Erdogan also said during a live televised address that the Netherlands would "pay the price".

The crisis with the Netherlands is the most serious yet as tensions spiral between Turkey and its EU allies over the desire of top Turkish officials to hold rallies abroad ahead of the April 16 referendum on a new constitution that would give Erdogan greater powers.

The Netherlands is home to some 400,000 people of Turkish origin, and Ankara is keen to harness their votes.

Family Minister Fatma Betul Sayan Kaya was expelled from the Netherlands after being prevented from addressing a rally in the Dutch port city of Rotterdam on Saturday.

The latest row came after NATO allies Turkey and Germany sparred over the cancellation of a series of referendum campaign events there.

"The West has clearly shown its true face in the last couple of days," Erdogan said. "What we have seen in the last days is a clear manifestation of Islamophobia."

READ MORE: Turkey tells Dutch ambassador: Don't hurry back

After the unprecedented diplomatic fight, Dutch Prime Minister Mark Rutte said on Sunday he would seek to control the damage caused by the weekend incidents. He denounced the comments about fascism.

"This country, as the mayor of Rotterdam pointed out yesterday, was bombed during the Second World War by the Nazis. It's totally unacceptable to talk in this way," Rutte said in The Hague.

The diplomatic fight comes at a tough time in the Netherlands, which has national elections on Wednesday, and where issues of Dutch identity and relations with migrant communities and Islam have taken centre stage.

In a neck-and-neck race, the parties of either Rutte or populist firebrand Geert Wilders could end up with the most votes.

Rutte said it was important for his government not to bow to Turkish pressure, especially, he said, after Ankara threatened sanctions if the Dutch kept its ministers out.

"Turkey is a proud nation; the Netherlands is a proud nation. We can never do business under those sorts of threats and blackmail," said Rutte.

Still, added the prime minister, his government "will keep working to de-escalate where we can. If the Turks choose to escalate, we will have to react, but we will do everything we can to de-escalate".

The Dutch foreign ministry said on Sunday that Turkish authorities are responsible for the safety of Dutch diplomats in Turkey.

Meanwhile, Denmark's Prime Minister Lars Lokke Rasmussen proposed on Sunday postponing a planned visit by Turkey's Prime Minister Binali Yilderim this month because of the diplomatic row between Turkey and the Netherlands.

France urged Turkey and several EU member states to calm tensions.