Remarks by South Africa's ambassador to the United States about President Donald Trump were "unacceptable," a State Department spokesperson told reporters on Monday after Washington last week made the decision to expel the envoy.

Ties between the two countries have slumped since Trump cut US financial aid to South Africa, citing disapproval of its land policy and its genocide case against Washington's ally Israel at the International Court of Justice.

The expulsion of ambassador Ebrahim Rasool following an article that quoted him as saying President Donald Trump was leading a white supremacist movement, was the last straw.

Secretary of State Marco Rubio said on Saturday in a post on X that he was expelling Rasool, calling him a "race-baiting politician" who hates Trump, and reposting the article from right-wing website Breitbart.

"These remarks were unacceptable to the United States, not just to the president, but to every American," State Department spokesperson Tammy Bruce, speaking at a daily briefing, told reporters.

"At the very least, what we should expect is a standard of some respect - basic, low-level respect - if you're in a position that is going to help facilitate any kind of diplomatic relationship with another country."

She added that Rasool's privileges as ambassador expired on Monday and he must leave the country by Friday.

South Africa's embassy in Washington did not immediately respond to a request for comment on the Breitbart article or Bruce's comments.

REVIEW OF TIES

South Africa previously called the expulsion regrettable in statements from its presidency and international relations department, but said it remained committed to building mutually beneficial relations.

Asked by reporters whether other ambassadors to the United States could criticise Trump without fear of being expelled, Bruce said: "You want people in each embassy who can actually facilitate a relationship."

Rasool presented his credentials to then-President Joe Biden on January 13, a week before Trump took office, according to the embassy's website. It was his second stint in Washington.

Bruce also said the Trump administration was conducting a serious review of Washington's South Africa policy, citing South Africa's land policy, its growing ties with countries like Russia and Iran and "aggressive positions" toward the US and allies, including accusing Israel of genocide.

Trump has said, without citing evidence, that South Africa is confiscating land and that "certain classes of people" were being treated very badly.

South African President Cyril Ramaphosa signed into law a bill in January aimed at making it easier for the state to expropriate land in the public interest, in some cases without compensating the owner.

Ramaphosa has defended the policy as evening out racial disparities in ownership in the Black-majority nation and said the government had not confiscated any land.