U.S. President-elect Donald Trump said in a newspaper interview published on Sunday that German Chancellor Angela Merkel had made a "catastrophic mistake" with a policy that let a wave of more than one million migrants into her country.

In a joint interview with the Times of London and the German newspaper Bild, Trump also said the European Union had become "a vehicle for Germany" and predicted that more EU member states would vote to leave the bloc as Britain did last June.

"I think she made one very catastrophic mistake, and that was taking all of these illegals," Trump said of Merkel, who in August 2015 decided to keep Germany's borders open for refugees, mostly Muslims, fleeing war zones in the Middle East.

"And nobody even knows where they come from. So I think she made a catastrophic mistake, very bad mistake," Trump said, adding that he always had "great respect" for Merkel and that he still viewed her as one of the most important world leaders.

Merkel faces a tough re-election battle in September.

Trump, who takes office on Friday, campaigned for president on promises of banning Muslims from entering the United States or imposing more severe restrictions on migrants from countries or regions with high levels of militant Islamist activity.

Trump said Germany had only recently gotten a clear impression of the consequences of Merkel's migration policy, without elaborating.

Last month, a 24-year-old Tunisian failed asylum-seeker drove a truck into a Berlin Christmas market, killing 12 people, before fleeing to Italy, where he was shot dead by police.

The attacker, Anis Amri, came to Germany in July 2015 after having spent four years in jail in Italy. That means he entered Europe before Merkel's August 2015 border decision.

In the interview, Trump said British voters would not have approved leaving the European Union had Europe not been engulfed in a migrant crisis.

Turning to his family's German roots, Trump said he was proud to have had ancestors from Germany and that he loved Germany. Asked about character traits he would link to his German roots, Trump said he liked order and strength.

The United States is Germany's most important trading partner, and Trump's protectionist talk has unnerved business leaders and exporters in Europe's biggest economy.

In the interview, Trump said the United States will impose a border tax of 35 percent on cars that German carmaker BMW plans to build at a new plant in Mexico and export to the U.S. market.