Obama's order maintains several sets of U.S. sanctions imposed since 1997 which restrict U.S. trade and investment with Sudan and block the assets of the Sudanese government and certain officials.

The United States had offered Khartoum the chance to put relations on a better footing if it cooperated with the January referendum that set South Sudan on the path to declare its independence on July 9.

While the vote went off relatively smoothly, Khartoum and the South Sudan government in Juba have remained at loggerheads over the main oil-producing border state of South Kordofan, where rebels and government forces have repeatedly clashed since June.

Violence has also broken out in Blue Nile and Abyei states, while U.S. officials say they have not seen sufficient progress in western Darfur region, where mainly non-Arab rebels took up arms against Khartoum in 2003 leading to a harsh government crackdown that Washington and some activists labeled genocide.