The Department of Homeland Security proposes to license its own family detention for migrants, part of an effort to dissuade illegal border crossings.
"All she had to do was say no," Trump said, adding that Frederiksen was "not very nice" in her refusal.
Trump's claim triggered a quick uproar from critics who said the Republican president was trading in anti-Semitic stereotypes. It came amid Trump's ongoing feud with Democratic congresswomen Ilhan Omar of Minnesota and Rashida Tlaib of Michigan, both Muslim. Trump has closely aligned himself with Israel, including its conservative prime minister Benjamin Netanyahu, while the Muslim lawmakers have been outspoken critics of Israel's treatment of the Palestinians.
President Donald Trump abruptly canceled a trip to Denmark on Tuesday after that country's prime minister dismissed his offer to buy Greenland as "absurd."