French President François Hollande | Dan Kitwood/Getty Images Theresa May, Angela Merkel among European leaders bashing Trump’s refugee move British prime minister says “we do not agree with this kind of approach.”

President Donald Trump's order to bar refugees and citizens from certain Muslim countries from the U.S. elicited growing criticism from European leaders, including British Prime Minister Theresa May and German Chancellor Angela Merkel.

Merkel's spokesman told Spiegel on Sunday that blanket restrictions aren't justified by the war on terror, saying the German leader "regrets" the ban and expressed her concerns in a telephone conversation with Trump on Saturday.

Shortly after meeting U.K. Prime Minister Theresa May on Friday, Trump signed an executive order canceling the arrival of refugees and asylum seekers for four months, and banning citizens of seven Muslim-majority countries from arriving in the country. Syrian refugees are also indefinitely restricted from coming to the country.

French President François Hollande on Saturday promised that he would have "a firm discussion" with Trump about it. At a summit of southern European countries in Lisbon on Saturday, Hollande also said that he was concerned by Trump's call for more countries to leave the EU, following in the footsteps of the U.K., and that EU countries had to respond to his rhetoric, according to Agence France Presse. Hollande spoke by phone with Trump later on Saturday.

During her stop in Ankara on the way back from a visit to the U.S., British Prime Minister Theresa May refused to condemn Trump's Muslim ban after being asked about it three times at a press conference with the Turkish prime minister on Saturday. "The United States is responsible for the United States' policy on refugees," she said. "The United Kingdom is responsible for the United Kingdom's policy on refugees."

But soon after midnight in London, May's spokesman put out a statement that "we do not agree with this kind of approach and it is not one we will be taking."

"We are studying this new executive order to see what it means and what the legal effects are, and in particular what the consequences are for U.K. nationals," the statement added. "If there is any impact on U.K. nationals then clearly we will make representations to the U.S. government about that."

London Mayor Sadiq Khan, a practicing Muslim, on Sunday morning called the ban "shameful and cruel."

President Trump's ban on refugees and immigrants from certain countries is shameful and cruel. https://t.co/ZuMaVoSq8p pic.twitter.com/USOymj8HUO — Sadiq Khan (@SadiqKhan) January 29, 2017

The mayor of Berlin, Michael Müller, in a statement criticized Trump's policies on migration, including his stated promise to build a wall along the Mexican border. "I call on the American President: remember your forerunner, Ronald Reagan. Remember his words: 'Tear down this wall'," he wrote. "And so I say: 'Mr. President, don't build this wall'."

The French were the most outspoken from the start.

"This can only worry us," Jean-Marc Ayrault, the French foreign minister, said at a press conference in Paris on Saturday, according to Reuters. Ayrault added that he and Germany's Vice Chancellor Sigmar Gabriel discussed their concerns over Trump's move. "Welcoming refugees who flee war and oppression is part of our duty," Ayrault said.

The liberal French presidential candidate Emmanuel Macron on Sunday also chimed in on Twitter:

I stand with the people fleeing war and persecution. I stand with the people defending our values #NoBanNoWall — Emmanuel Macron (@EmmanuelMacron) January 29, 2017

The United Nations refugee agency, UNHCR, and the International Organization for Migration also called on Trump to reconsider his decision, according to Reuters.

The two U.N. agencies said they hoped "that the U.S. will continue its strong leadership role and long tradition of protecting those who are fleeing conflict and persecution."

Meanwhile, Google told traveling staff to come back to the U.S. out of fear they wouldn't be granted re-entry into the country. At least 187 Google employees could be affected by Trump's order, said the company's CEO Sundar Pichai in a memo to the company, according to the Wall Street Journal.

This article was updated on Sunday.

Tom McTague in Ankara contributed reporting to this article.