The United States’ decision to expel South Africa's ambassador was "regrettable", the office of the president said on Saturday, urging "diplomatic decorum" between the two nations.

"The Presidency has noted the regrettable expulsion of South Africa’s Ambassador to the United States of America, Mr. Ebrahim Rasool," it said in a statement.

This comes after US Secretary of State Marco Rubio said the diplomat was no longer welcome because he was "a race-baiting politician" who hates the country and its president.

South Africa "was informed by the State Department yesterday that he had 72 hours to leave," AFP news agency reports, quoting South African foreign ministry.

The expulsion of Rasool, a former anti-apartheid campaigner, has added to rising tensions between Washington and Pretoria.

Trump in February froze US aid to South Africa, citing a law in the country that he alleges allows land to be seized from white farmers.

Last week, Trump further heightened tensions, saying South Africa's farmers were welcome to settle in the United States after repeating his accusations that the government was "confiscating" land from white people.

The Trump administration is also upset by South Africa’s case against Israel at the International Court of Justice, where Pretoria is accusing Tel Aviv of committing genocide against Palestinians in Gaza.