WASHINGTON President Barack Obama granted U.S. recognition of South Sudan as an independent state after it formally seceded from the north on Saturday.
But even as Obama hailed the "birth of a new nation" after South Sudan's official declaration of independence, he stopped short of announcing any immediate changes in longstanding U.S. sanctions on Sudan itself that Khartoum has been hoping will be lifted.
Obama's statement came amid jubilant celebrations in Juba, capital of the new Republic of South Sudan, an under-developed oil producer. It won its independence in a January referendum -- the climax of a 2005 peace deal that ended decades of civil war with the north.
"I am proud to declare that the United States formally recognizes the Republic of South Sudan as a sovereign and independent state upon this day, July 9, 2011," Obama said. "Today is a reminder that after the darkness of war, the light of a new dawn is possible."
But serious tensions remain between north and south and the fractured region now heads into a new period of uncertainty.
Northern and southern leaders have still not agreed on a list of issues, most importantly the line of the border, the ownership of the disputed Abyei region and how they will handle oil revenues, the lifeblood of both economies.
Obama made clear that more work needed to be done.
"Lasting peace will only be realized if all sides fulfill their responsibilities," he said. "The Comprehensive Peace Agreement must be fully implemented, the status of Abyei must be resolved through negotiations, and violence and intimidation in Southern Kordofan, especially by the government of Sudan, must end."
The Obama administration's strategy has been to offer Khartoum financial and diplomatic incentives in return for completing the north-south split in an orderly way.
But Obama made no specific promises as he welcomed South Sudan's independence and pledged U.S. partnership with the new nation in efforts toward security, development and good governance.
Secretary of State Hillary Clinton said South Sudan's independence marked an opportunity for Khartoum to demonstrate its commitment to resolving outstanding problems.
"By continuing on the path of peace, the government of Sudan can redefine its relationship with the international community and secure a more prosperous future for its people," Clinton said in a statement.
Washington has had a trade embargo on Sudan since 1997 and also lists the country as a state sponsor for terrorism. Khartoum has been hoping Washington would end all sanctions, normalize diplomatic relations and remove Sudan from the terrorism blacklist.
But U.S. officials remain concerned about the Sudanese government's harsh handling of insurgencies in its Darfur and South Kordofan regions.
(Reporting by Matt Spetalnick; additional reporting by Andrew Quinn; Editing by Vicki Allen)