ISTANBUL - A diplomatic crisis between Turkey and the Netherlands deepened on Monday as both sides traded bitter accusations after Turkish ministers were blocked from holding rallies to win support for plans to expand the powers of President Recep Tayyip Erdogan.

Erdogan at the weekend twice accused the Netherlands of acting like the Nazis, comments that sparked outrage in a country bombed and occupied by German forces in World War II.

Dutch Prime Minister Mark Rutte, who faces a major challenge from the far-right in a key general election Wednesday, said Erdogan's comments were unacceptable and it was Ankara that should apologize.

The Dutch authorities had at the weekend prevented the plane of Turkish Foreign Minister Mevlut Cavusoglu from landing and blocked Family Minister Fatma Betul Sayan Kaya from holding a rally in Rotterdam.

The ministers had been seeking to harness the support of an estimated 400,000 people of Turkish origin living in the country ahead of an April 16 referendum on constitutional changes giving Erdogan greater powers.

The Turkish Foreign Ministry on Monday summoned the Dutch envoy to Ankara for the third day in a row, handing two separate protest notes over the Dutch behavior.

The Netherlands on Monday issued a new travel warning to its citizens in Turkey, urging them to stay "alert across the whole of Turkey".

Turkey has already responded furiously to Germany's refusal to give permission for ministers to hold rallies there, with Erdogan comparing such action to "Nazi practices".

Denmark has also asked Turkish Prime Minister Binali Yildirim to postpone a visit planned for later this month.

The issue risks spiraling into a crisis with the EU as a whole, which Turkey has sought to join for more than half a century in a so far fruitless membership bid.

Erdogan, who has indicated he may attempt to address rallies in EU states in a move that could inflame the situation further, said on Sunday that the West was showing its "true face" in the standoff.

He has repeatedly accused the Netherlands of acting like "fascists" and "Nazis", saying on Sunday: "I had thought that the era of Nazism was over but I was wrong."

Rutte, under pressure to take a hard line against Erdogan as he faces the far-right populist Geert Wilders in Wednesday's poll, said there were no apologies to be made to Turkey.

"They (Turkey) should make excuses for what they've done yesterday," he said.

He expressed outrage at Erdogan's Nazi jibe, noting: "This country was bombed during the World War II by the Nazis. It's totally unacceptable to talk in this way."