Last-minute objections by Southern Sudanese leaders have forced another postponement of the fifth national census that had been scheduled for take place over two weeks from 15 April, officials said.

"We want the census to be comprehensive and inclusive and all areas of Sudan must be given an equal opportunity to participate," Southern Sudanese information and broadcasting minister Gabriel Changson Chang said.

"We will not be part of a flawed exercise; this is why we have decided to defer the census in Southern Sudan," he added. "The deferral will allow southerners to fully address issues that could have dogged the exercise."

The decision to pull out of the count, Chang said, was reached by the Southern Sudan council of ministers. The ministers raised objections regarding questions of ethnicity and religion, the demarcation of the north-south border, returns of displaced people and security.

"There are over two million internally displaced persons in Northern Sudan who have been obstructed from coming back to the South to be counted," Chang added. "The resources for repatriating them have not been forthcoming and some people have blocked the roads linking south with north."

The surprise move came despite assurances by the chairman of the Census and Statistics Commission, Isaiah Aruai Chol, that the exercise would proceed uninterrupted.

Chang, however, said they would like the exercise to be done within the year to ensure it did not affect elections planned for 2009.

"We want to know the size of our population because it is connected with the power- and wealth-sharing arrangement," he told reporters in the Southern capital of Juba. "We cannot allow our people to be counted as Northerners yet they are Southerners."

On security in disputed border areas, he said: "There have been skirmishes, women have been raped, men have been maimed and children defiled, while people have been abducted. This is a disruptive issue that cannot give you a desired result."

The official Sudan News Agency said President Omar el Bashir had decided the census should be postponed to 22 April following a meeting with Southern President Salva Kiir Mayardit.

Vice-President Ali Osman Mohamed Taha criticised the decision by Southern leaders, saying it contravened the spirit of the 2005 Comprehensive Peace Agreement that ended more than two decades of conflict between the North and South.

Late last year, the Southern leaders withdrew from the national coalition government, with the North citing various issues, including delays in census arrangements. They later returned to the government, but the mistrust between the two sides has remained high.

Sudan last conducted censuses in 1956, 1973, 1983 and 1993, with the last one due in 2003. Since then, the exercise has been delayed several times.

A spokesman for the Darfur rebel group, the Justice and Equality Movement, told UN radio Miraya that his group supported the postponement because many areas of Sudan, such as Darfur, were not safe enough.