Sudanese security agents released a correspondent for the pan-Arab newspaper Al-Hayat after holding him for six days in Khartoum, his family and the journalists' union said.

Al-Nur Ahmad al-Nur, who is also an editorial adviser for Sudanese daily Al-Tigheer, was at home with his family after being freed late on Wednesday, his brother told AFP.

Sudan's ruling party Monday named President Omar al-Bashir as a possible candidate for the country's April presidential elections, an adviser said, despite doubts he would stand again.

After taking power in an Islamist-backed coup in 1989, it had been unclear in recent years whether Bashir would run again in next year's polls.

The U.S. ambassador to the United Nations accused Sudan Thursday of intensifying attacks on civilians in South Kordofan and Blue Nile states, and of deliberately bombing schools and hospitals.

Samantha Power condemned "in the strongest possible terms" attacks she said were being carried out by the Sudanese government and its rapid support forces against ordinary people.

Sudan has carried out "unconscionable" violence including aerial strikes and aggression against civilians in its war-torn regions, the U.S. special envoy to the country charged Thursday.

A senior official from the ruling party in Khartoum disputed the allegation and said the envoy, Donald Booth, was not qualified to make such comments.

Police fired tear gas in the Sudanese capital on Monday when clashes between pro-government university students and their opponents spilled onto a downtown street, witnesses said.

"Both sides had steel bars, stones and chains and some of them clashed outside campus," said one student witness at the University of Khartoum. 

Khartoum dispatched reinforcements to its front lines Thursday as government and rebel delegations gathered in the Ethiopian capital to resume talks to end fighting in Sudan's South Kordofan and Blue Nile states.

The African Union-mediated negotiations aim to end the nearly three-year-old war in the two restive states, which aid groups say has left 1.2 million people in need of humanitarian assistance.

Sudan and rebels traded accusations on Monday but vowed to press ahead under African Union mediation with their first peace talks in nearly a year.

The United Nations has urged Khartoum and rebels from the Sudan People's Liberation Movement-North (SPLM-N), who began talks in the Ethiopian capital on Thursday, to declare an immediate ceasefire so aid can reach more than one million civilians.

The U.N. Thursday urged Sudan and rebels, meeting for their first peace talks in almost a year, to reach an immediate ceasefire so aid can reach more than one million civilians.

Negotiations between Khartoum and the Sudan People's Liberation Movement-North (SPLM-N) were to begin Thursday in the Ethiopian capital, Addis Ababa, under African Union mediation.

Sudan's President Omar al-Bashir will visit South Sudan Monday, state radio said, as negotiators in Ethiopia prepared formal ceasefire talks over three weeks of fighting in the world's youngest country.

Radio Omdurman said Sunday that Bashir would meet his southern counterpart, President Salva Kiir, in Juba for talks on the conflict in South Sudan, without giving further details.

The Sudanese government has agreed to let United Nations workers vaccinate tens of thousands of children against polio in the violence-wracked South Kordofan and Blue Nile states, the world body said Thursday.

United Nations Humanitarian Coordinator in Sudan Ali al-Zaatari said the vaccination campaign would begin on November 5.