Sudan's Foreign Minister Lam Akol (file photo)

The ruling party of southern Sudan has suspended participation in the national government, saying Khartoum has held up implementing the peace deal that ended Sudan's north-south civil war.

Officials with the Sudan People's Liberation Movement said Thursday that its 18 ministers in the central government will not report to work until key issues are resolved. Those ministers include Sudan's Foreign Affairs Minister, Lam Akol.

Party officials say the issues include a dispute over oil-producing areas, Khartoum's failure to withdraw troops from the south, and Sudan's progress toward democracy.

There has been no comment from the central Sudanese government.

The 2005 Comprehensive Peace Agreement ended 21 years of war in Sudan that killed an estimated two million people.

On Saturday, the U.S. special envoy to Sudan said Washington is "deeply concerned" about the state of the peace deal.

Envoy Andrew Natsios said important deadlines have been missed, and tensions in the north-south border areas are rising. Sudan's central government later condemned those statements, saying they were inaccurate and would not help narrow differences between the sides.

The Sudan People's Liberation Movement is the political wing of the southern rebels who fought the northern government.

The peace agreement set up a semi-autonomous government in the south and also laid out arrangements to share wealth and power. However, southern Sudanese officials have complained for months that Khartoum is obstructing implementation of the deal.

Southern Sudan is scheduled to hold a referendum in 2011 on whether to become an independent country.

Some information for this report was provided by AP and Reuters.