President Barack Obama's special envoy to Sudan and South Sudan is stepping down after two years on the job.

In a statement Monday, Obama praised Princeton Lyman for his role in helping South Sudan achieve independence. The president said the people of Sudan and South Sudan have the opportunity to "seize a brighter future" because of his envoy's efforts.

South Sudan, backed by the U.S., became an independent nation last year following a peace deal that ended years of civil war. Still, key disputes remain between the neighbors.

The White House said Obama plans to name a new special envoy to the region.