The Department of Commerce has allowed U.S. companies to deal with fiberglass company Steklovolokno and lacquer and paint producer Lakokraska, the official said.
Washington imposed sanctions against Belneftekhim and froze assets of its U.S. subsidiary last November, setting the release of all political prisoners in Belarus as a condition for lifting the sanctions.
The two firms were added to Washington's blacklist in May. The measures resulted in significant reductions of embassy staff in both countries.
Dialogue between Washington and Minsk reinvigorated after Belarus's main opposition figure, Alexander Kozulin, who was sentenced to a 5 1/2 year term for organizing protests against President Alexander Lukashenko, was released from prison in August.
The United States and the European Union have accused Lukashenko of clamping down on dissent, stifling the media and rigging elections. Lukashenko, who was re-elected to a third term in 2006, and other senior Belarusian officials have been barred from entering the U.S. and the EU.