An AU source said the talks were put off at the request of mediators, led by former Organisation of African Unity secretary general Salim Ahmed Salim, who was continuing separate consultations with representatives of the two Darfur rebel movements and the Khartoum government.

An AU statement referred to "consultations on several issues, relating to the agenda and programme of work as well as the format of the talks."

"The mediation team has also held meetings with Nigerian and Libyan facilitators as well as with international partners."

One AU source said that a delegation from Chad, Darfur's western neighbour, might join the talks, something which has been hitherto opposed by one of the rebel groups, the Justice and Equality Movement (JEM).

The fifth round of talks, and the first for six months, to end the war that has claimed between 180,000 and 300,000 lives and displaced 2.4 million people, formally opened here Friday.

The leaders of the two rebel groups, Mohammed Al-Nour of the Sudan Liberation Movement (SLM) and Ibrahim Khalil of the JEM, are attending for the first time, while Agriculture Minister Majzoub al-Khalifa continues to head the government side.

As the talks opened Friday, Sudanese forces attacked a garrison of AU peace monitors at El Fasher in Darfur and seized JEM members who were in the camp.

Nigerian General Festus Okonkwo, commander of the peacekeeping and observer mission of 2,700-member Nigerian and Rwandan troops said the JEM should have moved its men out earlier.

An expanded mission force of 6,171 men is set to be in place by September, including military observers and peacekeepers and a civilian police contingent of 1,560.

The Abuja talks will take place behind closed doors in the presence of international observers. AU officials have said they did not expect them to last beyond three weeks.

The talks which began in August 2004 were suspended in December to allow for more consultations among the warring parties, who were accusing each other of violating ceasefire agreements.

Violence broke out in Darfur in February 2003 when a rebel uprising against the government led Khartoum to unleash Arab militias known as Janjaweed on a scorched-earth campaign.

The Janjaweed in particular are accused of "ethnic cleansing", torture, rape and intimidation.

Humanitarian officials have warned the situation in Darfur is growing more desperate, with not enough funding to meet the crisis caused by drought, famine and the long-term effects of conflict.