U.S. officials say President Bush's special envoy for Sudan, Andrew Natsios, has resigned.
The officials, speaking on condition of anonymity, told reporters of the resignation Friday. They said the White House will make a formal announcement.
Natsios was appointed to the envoy post in September 2006 and had spent considerable time trying to end the violence in Sudan's Darfur region.
Efforts to start peace talks between Sudan's government and Darfur rebel groups have stalled, while Sudan continues to negotiate conditions for deploying a U.N.-African peacekeeping force in the region.
Natsios previously served as administrator of the main U.S. foreign aid program, the U.S. Agency for International Development.
Some information for this report was provided by AP and Reuters.