Trump tweeted Sunday that the liberal Democrats should go back to the "broken and crime infested" countries they came from. All four are American citizens and three were born in the United States.
May, who is set to step down next week following her resignation over Brexit, thinks "the language which was used to refer to the women was completely unacceptable," spokesman James Slack said.
Boris Johnson and Foreign Secretary Jeremy Hunt, the two politicians in the runoff to replace May as Conservative Party leader and U.K. prime minister, agreed.
Johnson said Trump's remarks were "totally unacceptable in a modern multiracial country."
"If you are the leader of a great multiracial, multicultural society, you simply cannot use that kind of language about sending people back to where they came from," he said during a debate with Hunt.
His political rival echoed the sentiment.
"I have three half-Chinese children," said Hunt, whose wife is Chinese. "And if anyone ever said to them, 'Go back to China,' I would be utterly appalled."
But Hunt - who as foreign secretary is Britain's top diplomat - balked when asked whether he would call Trump's comments racist, instead noting that the United States is Britain's closest ally.
"It is not going to help the situation to use that kind of language about the president of the United States," he said
Johnson declined to answer when he also was asked if Trump's words were racist.
The comments come at a testy time for U.K.-U.S. relations. The trans-Atlantic relationship has been rattled in the last two weeks by the Mail on Sunday newspaper's publication of leaked diplomatic cables from Britain's ambassador in Washington criticizing the Trump administration.
Trump responded by calling Ambassador Kim Darroch "very stupid" on Twitter and cold-shouldering him. Darroch resigned, saying he could no longer do his job.
Trump defended his tweets about the congresswomen, taking to Twitter again Monday to demand apologies from the four Democrats and claiming "so many people are angry at them and & their horrible & disgusting actions."
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