The census, earlier scheduled to run from 5 to 30 April, is an important milestone in implementing the 2005 Comprehensive Peace Agreement, which ended a decades-long civil war between the Government and rebels in southern Sudan, a conflict separate from the ongoing fighting in the Darfur region in the country's west.

“The Secretary-General expresses the hope that the census will not be further delayed, as it could have considerable political and financial implications,” as statement issued by Mr. Ban's spokesperson said.

“The Sudanese people, with the assistance of the international community, have invested much in the preparation of the census and look forward to a full and peaceful enumeration process.”

In February, Mr. Ban's Special Representative to Sudan Ashraf Qazi told the Security Council that implementation of the agreement ending 21 years of war, in which as many as 2 million people were killed and 4.5 million others displaced, remained on track despite being behind schedule.

He said overall security in the ceasefire zone remained relatively stable, but tensions between the Sudanese Armed Forces and the Sudan People's Liberation Army (SPLA) actually increased along the current boundary between northern and southern Sudan.

He warned that while the working relationship between the two parties was relatively cordial, it suffered from a significant lack of trust and confidence.

The most recent UN report on implementing the agreement found that major challenges lie ahead, but praised the leaders of both sides for demonstrating a willingness to resolve their differences through dialogue.

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Peace accord between north and south Sudan still on track, says UN envoy