Former southern Sudan rebels recalled their ministers from the national Sudanese government to protest peace treaty violations, the party's chief said Thursday in the most dangerous blow yet to a fragile peace deal that ended two decades of civil war.

Observers have warned for months that the 2005 Comprehensive Peace Agreement between the north and south could collapse because of implementation delays. A new civil war between the two could plunge all of Sudan into chaos and further worsen the violence in the western Darfur region, they say.

"We are working to avoid a return to war, that is the essence of the management of the current crisis," party secretary general Pagan Amum said in an interview with The Associated Press, insisting the ministers' pullout was not a step toward renewed conflict but a political measure.

"We want to make sure the CPA is implemented rather than dishonored," he added.

The Sudan People's Liberation Movement accuses Khartoum of multiple breaches of the 2005 deal, including not sharing the country's oil wealth as agreed, not pulling troops out of southern Sudan, and remilitarizing contested border zones where the main oil reserves are located.

"The SPLM has recalled all ministers and all presidential advisers to the government of national unity," Amum told AP in Juba, which serves as the south's capital. He said the measure was effective immediately.

The 2005 agreement ended two decades of civil war between the Arab and Muslim-dominated north and the mainly Christian and animist black southerners. Africa's bloodiest conflict, the war caused the death of some 2 million people.

Under the peace agreement, southerners hold about a third of the positions in Sudan's government. Prominent officials include Sudanese Vice-President Salva Kiir, also president of southern Sudan, and Lam Akol, Sudan's minister of foreign affairs.

Amum said the SPLM's 18 Cabinet ministers and three advisers in the central government "will not report to work until the contentious issues are resolved."

"We hold President Bashir and the whole NCP (northern) leadership personally responsible for the violations," he said. "These aren't delays, these are flagrant violations."

"We are urging the (U.N.) Security Council to call a meeting" to assess the peace deal's problems, Amum added. The United Nations mission to Sudan had no immediate comment, but has repeatedly warned of delays in implementing the agreement.

The U.S. embassy said it was aware of the southerners' pullout, and insisted Thursday it continued to support the unity of Sudan as a whole.

The south's surprise measure seemed to catch Khartoum officials off guard, with many refusing to comment.

"I have no comment, this is not a foreign affairs issue," said Ambassador Ali Sadiq, the spokesman for a now leaderless ministry. He said officials from the North's all-powerful National Congress Party would decide how to react. NCP officials did not immediately return phone calls.

Sadiq said the foreign ministry would remain operational even in its leader's absence. "We have two state ministers, they'll be in charge, that's how the ministry works," he said.

The ministry's two junior ministers are both northern Arabs and members of the president's NCP party. Southerners have long accused the NCP of creating parallel command structures in Khartoum to give southerners government positions required by the peace deal while retaining true control.

Sudan, Africa's largest country, has been dominated by a small elite of northern Arab tribes since its independence from Britain in 1956.

Khartoum's hardline Arab elite has "its own power system," Amum said. Without the balance brought to the government by the former southern rebels, "They will go back to their old ways, which is the way of dictatorship," he said.

The government of President Omar al-Bashir came to power in a military and Islamist coup in 1989, and there have been no elections since.

Amum did not specify whether the SPLM had issued advice to the large population of southerners who live in refugee camps on the outskirts of Khartoum and who have protested in the past when incidents broke out between the north and south.

"We are calling on all the people for Sudan to rally behind the objectives of the CPA and of democracy," Amum said.

The peace deal provides for nationwide general elections in early 2009, and a southern referendum on independence in 2011. But the census necessary for these votes has already been postponed once.

The U.N. and U.S.-brokered agreement that ended the southern civil war was a major diplomatic victory and fueled hopes that the Darfur conflict could be similarly 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 the Arab janjaweed militias, which are blamed for atrocities against ethnic African villagers. More than 200,000 people have been killed and 2.5 million driven from their homes in the conflict.

The gravity of the situation in Darfur was highlighted Thursday with a U.N. statement citing reports of dozens of civilians killed, injured or missing in the rebel-held town of Muhajeria that was attacked by Arab militias earlier this week.

The U.N. said the town was partly burned and looted and that its 20,000 inhabitants had fled. Rebels have said at least 48 were killed in the government attack, and aid groups counted at least 40 seriously injured.

Clashes between rebel and government forces were also reported in several other parts of Darfur, prompting aid and U.N. workers to pull out of those areas. The U.S. Embassy also said it was temporarily pulling all of its staff out of Darfur for security reasons.