Princeton Lyman, US special envoy to Sudan and South Sudan, is leaving his post, less than two weeks after warning that distrust between the two states was undermining crucial security and oil pacts.
President Barack Obama announced Lyman's departure in a statement, praising him for doing a "tremendous job" in realizing the promise of an independent South Sudan and of working toward two states "living side by side in peace."
"The people of Sudan and South Sudan, who have suffered so much, have the opportunity to seize a brighter future because of Princeton's efforts to urge both sides to put the interests of their people first," Obama said.
"I am deeply grateful for Princeton's steadfast and tireless leadership."
A White House source said that it was unclear so far whether Lyman would be replaced, but styled his departure as the kind of personnel change that is normal at the end of a president's first term and start of a second.
Lyman, 77, an author and Africa expert, had a long diplomatic career when he was named as special envoy. He served as deputy assistant secretary of state for African Affairs and as US ambassador to Nigeria.
He was also US ambassador to South Africa (1992-1995) and assistant secretary of state for international organizational affairs between 1996 and 1998.
Under a peace deal that ended a 1983-2005 civil war, South Sudan became independent last year.
The neighbors fought along their undemarcated frontier in March and April, sparking fears of wider war and prompting a UN Security Council resolution ordering a ceasefire and African Union mediation.
They reached security and cooperation deals in September, but the implementation has been delayed, prompting Lyman's warnings.
He told reporters last month that obtaining trust between the two sides would be difficult unless an insurgency -- allegedly backed by South Sudan -- ends in Sudan's border states of South Kordofan and Blue Nile.
"I think what happened in the process so far is that they haven't reached that degree of confidence and trust which is essential in carrying out this type of agreement," Lyman said after talks in Khartoum with Sudanese officials.© ANP/AFP