Sudan's former leader Sadiq al-Mahdi held an unusual show of force on Saturday, telling thousands of followers that the regime of President Omar al-Bashir has to go, 24 years after it toppled Mahdi.

"From today, we will sign on to the ticket of liberation to have a new regime," Mahdi told his faithful gathered on a sandy outdoor square in Khartoum's twin city of Omdurman.

Deadly battles have again erupted in Sudan's Darfur between two Arab tribes which began fighting in January over control of gold mining, sources from both sides said on Thursday.

A leader of the Beni Hussein tribe told Agence France Presse the rival Rezeigat group attacked outside El Sireaf town in the Jebel Amir region of North Darfur state on Wednesday.

Twelve Sudanese were killed on Sunday when a wall collapsed as thousands crowded to submit their applications for the annual hajj pilgrimage, witnesses said.

More than 4,000 had gathered at a government office in Gedaref town southeast of the capital Khartoum, said one witness who asked to remain anonymous.

Newly-displaced people in Sudan's South Darfur are living in "terrible" conditions and need help to avoid a humanitarian disaster, a United Nations expert said on Thursday.

Mashood Baderin, the U.N.'s independent expert on human rights in Sudan, visited South Darfur's Otash camp during his latest mission to the country.

Shells hit a United Nations base in Sudan's troubled South Kordofan state on Friday, killing one peacekeeper and wounding two more, a U.N. spokesman said.

Two shells struck a U.N. logistics base in South Kordofan's main city Kadugli, U.N. peacekeeping spokesman Kieran Dwyer told Agence France Presse. Rebels have been fighting Sudanese forces in the state for the past two years and the U.N. says there is a major humanitarian crisis there.

Egyptian President Mohammed Morsi has warned that "all options are open" in confronting an Ethiopian project to build a dam on the Blue Nile, which may diminish Egypt's water supply.

"I confirm that all options are open to deal with this subject," the Islamist president told hundreds of his supporters late Monday at a conference on the issue.

A Sudanese nurse working for an international aid agency in Sudan's troubled Darfur region has been shot dead during a gun battle inside a camp for displaced people, humanitarian workers said on Tuesday.

It is the first known death of an aid worker in Sudan since a Sudanese driver for the United Nations World Food Program was killed during an attack in war-torn South Kordofan state last August.

The Sudanese armed forces burned and shot civilians to death in a "scorched earth" campaign against a rebel chief's home district in Blue Nile state, Amnesty International said on Tuesday.

Satellite imagery confirms that the attacks in Blue Nile's Ingessana Hills, the birthplace of rebel chairman Malik Agar, occurred in the first half of last year, the London-based watchdog said in a 74-page report.

South Sudanese President Salva Kiir said Monday he would refer oil arguments with arch-rivals Sudan to African Union mediators, vowing not to take the country back to war.

"The people of South Sudan should remain calm and patient as we work with the African Union to resolve this impasse with Sudan," Kiir told reporters, while condemning the "aggressive attitude" of Khartoum.

Sudan on Sunday put on hold nine security and economic pacts with South Sudan, including on vital oil shipments, but said Khartoum remained committed to good relations if Juba ended support for rebels.

"We will stop all nine agreements, not only oil," Information Minister Ahmed Bilal Osman said at a news conference.