UK prime minister hopefuls slam Trump tweets -- but refuse to call them racist

The two candidates vying to become Britain's next prime minister both condemned on Monday US President Donald Trump's xenophobic tweets about progressive Democrat congresswomen as "totally offensive" and "totally unacceptable".

But front-runner Boris Johnson and Foreign Secretary Jeremy Hunt refused to call the tweets racist when pressed to do so during their last debate before next week's announcement of who will succeed Prime Minister Theresa May.

May's spokesman had earlier said that the outgoing leader's view was that Trump's comments were "completely unacceptable".

On Monday Trump doubled down on a series of his tweets from the day before urging the four congresswomen of colour to "go back" to the countries they came from.

"If you're not happy here, you can leave," Trump told reporters at the White House.

Johnson said the original tweets expressed sentiments "that went out decades and decades ago".

"I think the relations between the UK and US are incredibly important," said Johnson.

"But if you are the leader of a great multiracial, multicultural society, you simply cannot use that kind of language about sending people back where they came from," Johnson said.

"It's totally unacceptable and I agree with the prime minister."

Trump has developed good relations with Johnson and backs both his leadership bid and determination to take Britain out of EU.

Pressed by the moderator to call Trump's tweets racist, Johnson said: "I've said what I said."

Hunt recalled that he had three half-ethnically Chinese children who are British citizens.

"If anyone said to them, go back to China, I would be utterly appalled," Hunt said.

"It is totally un-British to say that."

Pressed to call the comments racist, Hunt signalled that he would have were he not Britain's chief diplomat.

"Look, I am foreign secretary, this is the president of a country which happens to be our closest ally and so it is not gonna help the situation to use that kind of language about the president of the United States," Hunt said.

"I can understand how many people of this country would want me to use those words, and would feel that sentiment," he added.

"But I hope I have made absolutely clear how totally offensive it is to me that people are still saying that kind of thing."

Some 160,000 paying members of the ruling Conservative Party are currently picking the country's new leader.

The winner of the mail-in ballot will be announced on July 23. The new prime minister formally assumes office the following day.