South Sudan celebrated its inaugural Independence Day during the weekend. Independence was part of a peace agreement brokered with Washington's help in 2005.
British Foreign Secretary William Hague said London welcomed South Sudan's independence as a historic moment for Africa.
"This is an African solution to an African problem and shows how conflict can be resolved through negotiation," he said in a statement.
Susan Rice, the U.S. ambassador to the United Nations, led a U.S. delegation to Independence Day celebrations in Juba. She said there should be no disillusionment about the difficulties ahead for South Sudan.
"No true friend would offer false comfort," she said in her statement. "The path ahead will be steep and pitted."
Ethiopia offered to send peacekeepers to the border region to help calm regional tensions. Border conflicts centered near Abyei and South Kordofan state threatened to unravel the Sudanese peace agreement.
"We continue to urge both countries to display the necessary leadership and spirit of compromise to reach a negotiated settlement to all outstanding issues as soon as possible, so that their citizens may enjoy the peace, stability and prosperity they deserve," Hague said after returning from South Sudan.