US President Donald Trump's nominee for ambassador to South Africa has refused to tell US senators if he would support or oppose the reinstitution of laws in the US allowing only white people to vote.

Leo Brent Bozell III, a member of a famous conservative family, was being grilled on Thursday by Democratic Party senators about his views on race and other issues during his confirmation hearing before the Senate Foreign Relations Committee.

Senator Chris van Hollen quizzed him about Trump's policy of encouraging white Afrikaners to get refugee status in the US on the grounds that a genocide was being conducted against them in South Africa.

Van Hollen asked Bozell if he agreed with Trump's "legally and morally absurd claim that the government of South Africa was engaged in genocide against Afrikaners there". Bozell declined to answer the question directly. When Van Hollen demanded a simple yes or no, insisting that "genocide is a legally defined issue", Bozell replied: "I'm not a lawyer, so I can't address it that way."

Van Hollen went on to say that Trump was reported to be reducing the number of refugees that can come into the US to around 7,500, “and that the overwhelming majority of those would be Afrikaners, white South Africans.