US President Donald Trump has publicly criticized South Africa's President Cyril Ramaphosa, alleging that the white minority is being persecuted in his country.

The United States announced a freeze on aid to South Africa after its government introduced a new policy on land expropriation.

The Trump administration claims the policy threatens the rights of the white minority and is discriminatory.

Trump met Ramaphosa at the White House on Wednesday. The summit began in a congenial atmosphere, with Ramaphosa expressing hope of mending bilateral relations by promoting trade and investment.

But the mood changed when Trump played a video of what he described as people urging others to attack whites.

Trump also showed papers that he said were articles that proved whites are being persecuted and even killed.

Ramaphosa admitted there are criminal activities in South Africa, but said the majority of those killed are Black. He denied that white people are being racially persecuted.

The focus of the summit had been whether the US could improve ties with South Africa, which chairs the G20 this year.

But Trump's remarks have only underscored their differences.