The U.S. special envoy to Sudan, Andrew Natsios, has warned of what he calls a "poisonous" political atmosphere between Sudan's government in the north and rebels in the south.

Natsios Saturday said the U.S. is deeply concerned about the health of the Comprehensive Peace Agreement signed in 2005. He made the comments as he wrapped up a 10-day visit to Sudan.

That agreement ended the two decade-long civil war between the government in Khartoum and southern rebels. Both sides have been critical of each other over missed deadlines for implementing key parts of the accord.

The agreement makes both sides partners in resolving the conflict in Darfur. But Natsios said implementation has been made difficult, in part, because both parties are facing one another in elections slated for 2009.

Some information for this report provided by AP, AFP and Reuters.