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

Secretary of State Marco Rubio said Friday that ambassador Ebrahim Rasool was no longer welcome in the United States because he was "a race-baiting politician" who hates US President Donald Trump.

"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

"The Presidency urges all relevant and impacted stakeholders to maintain the established diplomatic decorum in their engagement with the matter."

"South Africa remains committed to building a mutually beneficial relationship with the United States of America," the presidency said.

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.