South Africa's President Cyril Ramaphosa has told G20 foreign ministers that a commitment to multilateralism and international law is vital to solving global crises.

His comments follow growing concern about the Trump administration's "America First" policy, with US Secretary of State Marco Rubio boycotting the meeting and Treasury Secretary Scott Bessent saying he will not attend next week's gathering of G20 finance ministers.

Rubio said he would not "coddle anti-Americanism", while Bessent said he had other commitments in Washington.

South Africa is the first African state to lead the G20, hoping to advance the interests of developing nations in talks with the world's richest states.

The G20 consists of 19 countries, along with the African Union (AU) and European Union (EU), and makes up more than 80% of the global economy and two-thirds of the world population.

The foreign ministers of China, Russia, France and the UK are among those attending the meeting in Johannesburg, while the US is represented by the deputy chief of mission at its South African embassy.

In his opening address, Ramaphosa said that an "already fragile global coexistence" was threatened by rising intolerance, conflicts and climate change.

"Yet there is a lack of consensus among major powers, including in the G20, on how to respond to these issues of global significance," the South African president said.

"It is critical that the principles of the UN Charter, multilateralism and international law should remain at the centre of all our endeavour," he added.

South Africa holds the G20 presidency until November 2025, when it is expected to hand it over to the US.

Relations between the two countries have become increasingly strained since President Donald Trump took office in January, raising questions about how much South Africa can achieve during its presidency.

Trump has cut aid to the country, accusing it of "unjust and immoral practices" against the white minority Afrikaner community and by filing a genocide case against Israel in the International Court of Justice (ICJ) in December 2023.

His decision was followed by Rubio saying he would not attend the meeting of foreign ministers because South Africa was "doing very bad things", using the G20 "to promote 'solidarity, equality, & sustainability.' In other words: DEI [diversity, equity and inclusion] and climate change".

In a post on X, he added: "My job is to advance America's national interests, not waste taxpayer money or coddle anti-Americanism."