The national unity government was supposed to have been in place by August 9, but its formation was disrupted by the death in a July 30 helicopter crash of southern leader and first vice president John Garang.

While agreements have been reached on the distribution of most portfolios according to power-sharing quotas set in a landmark January peace deal, the energy and mining ministry was still being hotly contested.

Both the ruling National Congress and the former southern rebels want control over oil resources, one of the main factors that fuelled the 21-year civil war between the Muslim-dominated Khartoum regime and the mainly Christian or animist south.

"The National Congress and the Sudan People's Liberation Movement have agreed on sharing the sovereignty portfolios, but there are still consultations on the economic ones, particularly the energy and mining portfolio," the ruling party's deputy chairman Ali Nafie told the official SUNA news agency.

"I hope we can reach a full agreement in order to form the national unity government."

Sudanese President Omar al-Beshir and First Vice President Salva Kiir -- who succeeded John Garang as former rebel leader -- were holding talks on a range of issues Sunday, including the future government line-up.

Kiir conceded during a recent visit to south Sudan that both the National Congress and the former rebels wanted the key energy portfolio, but insisted the disagreement would not derail implementation of the peace process.

The presidential spokesman agreed that arguments over ministries would not be allowed to derail the peace process.

"What matters is that the two peace partners are determined to implement the peace agreement," said Badri.

Under the quotas set out in January's peace deal, 52 percent of executive and legislative posts are reserved for the National Congress, 28 percent for the former rebels, 14 percent for the northern opposition and six percent for dissident southern groups.

Many northern opposition factions have rejected the quotas, including the Umma party of former premier Sadiq al-Madhi and the Popular Congress of Islamist leader Hassan al-Turabi.

They have also declined to join the national unity government, saying that their representation would be merely token.

"Any participation will be for decoration," said Popular Congress political sectretary Beshir Adam Rahma, complaining that the only cabinet posts on offer to factions not party to the January peace deal were "marginal" ones such as animal resources and environment.

"We will be in the opposition," until new elections due in four year time, Rahma told AFP.