The United States is worried that a peace agreement between Northern and Southern Sudan could be jeopardized by a law passed by Sudan's parliament.
A 2005 agreement established peace after a decadeslong war and established a 2011 referendum on possible independence for the South. State Department spokesman Ian Kelly says a law passed Tuesday on the terms of the referendum reneged on an agreement by the two sides this month.
He said Wednesday that the move "undermines the peace process."
Representatives from the main Southern political party, the Sudan People's Liberation Movement, walked out of the Sudanese Parliament before the vote.
Kelly also criticized passage of a new national security law Tuesday that he said did not deal with concerns about the country's security services, which have cracked down on opposition and restricted free speech.
Sudan's civil war ended with the 2005 Comprehensive Peace Agreement that set up a national unity government, established an autonomous south and stipulated the holding of the referendum to determine the future of the south.
The agreement also dictates that all Sudanese parties work for unity before the referendum. But the partnership has been rocky, mostly because of mutual distrust between the former rivals.
One analyst, John Prendergast, co-founder of Enough!, said the SPLM's walkout Tuesday was a step toward the breakdown of the national unity government.
"This is a political shot across the bow that augurs the potential for a military one within the next year," he said.