A US House committee will on Wednesday consider a three-year extension to Washington's flagship trade initiative for Africa which lapsed in September, but South Africa risks being excluded amid tensions between Pretoria and the Trump administration.

Ties have deteriorated this year with a row over trade and as President Donald Trump has frequently criticised South Africa for its domestic laws addressing racial inequality.

The House committee meeting is the most significant progress Congress has made towards renewing the African Growth and Opportunity Act (AGOA), but its ultimate prospects remain unclear.

The law was first enacted in 2000 to provide duty-free access to the US market for eligible Sub-Saharan countries and products, and hundreds of thousands of African jobs are estimated to depend on it.

US Trade Representative Jamieson Greer said on Tuesday the Trump administration was open to a one-year extension but might exclude South Africa, which he described as a "unique problem".

He said South Africa needed to lower tariffs and non-tariff barriers on US products in order for the US to reduce its 30% duties on South African goods. South Africa has previously said the Trump administration based its tariffs on an inaccurate view of the two countries' trade.

There is no special provision for South Africa in the current draft of the AGOA Extension Act, but the US House Committee on Ways and Means will consider amendments to the text before voting on whether or not to send it to the full House of Representatives.

Another bill introduced in the Senate in October proposes a two-year renewal of AGOA and a review of the bilateral relationship with South Africa, but it has not yet been taken up in committee.

South Africa's trade ministry spokesperson told Reuters the country was committed to ensuring it is included in AGOA if it is extended.