World leaders gathered Saturday for a historic first Group of 20 summit in Africa that aims to put the problems of poor countries at the top of the global agenda.

But the talks have been undermined by a rift between host South Africa and the United States over a Trump administration boycott.

The weekend summit in Johannesburg will be attended by delegations from 18 of the world's richest and top developing economies — minus the U.S., which has branded South Africa's hosting a “disgrace" and won't participate in the talks.

The boycott by the world's biggest economy and founding G20 member was ordered by U.S. President Donald Trump over his claims that majority-Black South Africa is persecuting its white Afrikaner minority.