JUBA, Sudan — Southern Sudan’s former rebels yesterday suspended participation in the central government, accusing it of failing to abide by a peace deal in a dispute that threatens a rare success in the troubled nation.

American officials and other international observers have warned that a 2005 peace agreement between Sudan’s north and south was in danger of unraveling, threatening a new civil war that could also dash hopes for ending a separate conflict in western Darfur.

The Sudan People’s Liberation Movement said it was withdrawing its 18 Cabinet ministers, including the foreign minister and the vice president, and three advisers.

Pagan Amum, the party secretary-general, said the decision was not intended to renew conflict but to push for better implementation of the 2005 Comprehensive Peace Agreement. “We are working to avoid a return to war,” he told the Associated Press. “We want to make sure the CPA is implemented rather than dishonored.”

The People’s Liberation Movement accuses the Khartoum government of multiple breaches of the peace deal, including not sharing oil wealth, failing to pull troops out of the south, and remilitarizing contested border zones where the main oil reserves are located. The 2005 agreement ended two decades of civil war between the Arab and Muslim-dominated north and the mainly Christian and animist black southerners. The war, Africa’s bloodiest conflict, left about 2 million people dead in fighting, related disease, or famine.

Mr. Amum urged the U.N. Security Council to meet to examine the peace deal’s problems. “These aren’t delays, these are flagrant violations,” he said.

There was no comment from the government in Khartoum, which seemed to have been caught by surprise by the decision.

A small elite of northern Arab tribes has dominated Sudan since its independence from Britain in 1956. The U.N.- and American-brokered agreement that ended the southern civil war was a diplomatic victory and fueled hopes that the Darfur conflict could be resolved. But the four-year-old crisis in Darfur has only worsened between government forces and ethnic African rebels. The government is accused of unleashing Arab militias, known as the Janjaweed, blamed for atrocities against black African villagers.