The customs group includes Botswana, Lesotho, Namibia, South Africa and Swaziland.
"The (US) administration is committed to bringing back trade agreements that open markets to benefit our farmers, workers, businesses, and families," Zoellick said in a letter to Congress.
"With the Congress' continued help, we can move promptly to advance America's trade interests. We are responding to Congress' direction, as expressed in the African Growth and Opportunity Act, to initiate negotiations with interested beneficiary countries to serve as the catalyst for increasing free trade between the United States and sub-Saharan Africa and for increasing private sector investment in the region."
The move comes amid criticism from the World Bank and others that rich nations are putting up trade barriers to the poorest countries, making it hard for the poor to benefit from globalisation.
US exports to the customs union countries was about $3.1bn in 2001 and total two-way trade between was approximately 7.9 billion, the USTR office said.
The USTR has recently indicated it would start free-trade talks with Morocco and five nations of Central America. In addition, Zoellick also notified Congress of the US intention to complete free trade negotiations with Singapore and Chile and the Free Trade Area of the Americas. - Sapa-AFP