Sudan's south said a census vital to sharing wealth and power with its former northern foe would not take place until questions on ethnicity and religion - major issues behind decades of civil war - were included.

The semi-autonomous south withdrew from the census on Saturday three days before it was due to begin, saying the north-south border needed to be demarcated and southerners living in the north needed to return home before it began.

The northern National Congress Party (NCP) said a delay in the census - needed to define constituencies - could push back Sudan's first democratic elections in 23 years due in 2009.

But South Sudanese Vice President Riek Machar said the south would not participate without the ethnicity and race questions and his wife, who is also a state minister, said the election could go ahead.

"Ethnicity and religion are crucial issues. They address the identity of Sudan," Machar told Reuters. "Our wars are based on (the question:) What is Sudan?"

Sudan's national cabinet, including southern and northern ministers, debated the census on Sunday but one source inside the meeting said both sides stuck firm to their positions.

"(The cabinet) invited the government of southern Sudan to retract its decision on delaying the population census," Information Minister al-Zahawi Ibrahim Malik told reporters in Khartoum after the meeting.

He said any decision on whether the census would go ahead in the north without the south would be taken by the presidency.

First Vice President southerner Salva Kiir is to arrive in Khartoum on Monday to have crisis talks with President Omar Hassan al-Bashir, one source in the government said.


VOTE DELAY?

The NCP said the return of displaced southerners and marking the north-south border were not conditions that had to be met before the census, state news agency SUNA reported. The south had also already agreed to alternatives to questions on ethnicity and religion, according to a letter seen by Reuters.

Machar's wife, State Minister of Energy Angelina Teny, dismissed NCP warnings that the vote could be postponed, saying "We can mark out the constituencies in the first four months of next year so it really shouldn't delay the elections".

Machar said the delay would give the two sides time to resolve key outstanding issues like demarcating the north-south border and gaining access to Sudan's western Darfur region, where rebels took up arms in 2003 displacing almost half the population and creating anarchic security conditions.

The imposition of Islamic sharia law in 1983 fuelled Sudan's civil war. The former rebels say the south is mainly Christian or animist whereas some in the north say there are more Muslims in the south.

The war claimed 2 million lives and forced more than 4 million from their homes. The 2005 deal does not cover the Darfur conflict. Darfur's rebel groups have rejected the census, as have many Darfuris living in camps in the remote west.