The U.S. State Department said on Monday that the United States is optimistic about the upcoming referendum in Sudan.

"At this point, we are optimistic about the referendum this coming weekend," said State Department spokesman Philip Crowley at a daily briefing, referring to the referendum due to be held on Sunday in south Sudan.

But Crowley admitted that in terms of this political process, " there is still a long way to go and a difficult road ahead."

Stipulated by the Comprehensive Peace Agreement (CPA) inked between north and south Sudan in January 2005, the southern Sudanese are expected to head for the voting booths on Sunday, to decide whether the region should remain united with north Sudan or secede to establish an independent state.