The UN urged the Sudanese government and rebels, meeting Thursday for their first peace talks in almost a year, to declare 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 open in the Ethiopian capital, Addis Ababa, later on Thursday under African Union mediation.

AU officials held separate meetings with the two sides during the morning to draw up the agenda.

"Both parties in these talks are urged to declare an immediate cessation of hostilities allowing humanitarian teams to provide much needed support to these areas," the head of the UN mission in Sudan, Ali Al-Za'tari, said in a statement.

There are no reliable figures for how many people have died in the Kordofan region and Blue Nile state, where the SPLM-N has been fighting for nearly three years, drawing support from among their non-Arab populations.

The UN says an estimated 1.2 million have been displaced or otherwise affected in the two areas which both lie on the South Sudan border.

Late Wednesday, state radio said a landmine blast in South Kordofan killed five people and wounded 13. The report could not be verified.

Sudanese authorities have restricted access to the war zones for aid workers, journalists and foreign diplomats, although relief has reached people in government-controlled zones.

There has been no aid access into SPLM-N areas from within Sudan since 2011, and a senior UN official last year said people were surviving on roots and leaves.

"I urge both parties to ensure that the welfare of civilians in these states is an absolute priority during these talks," Za'tari said.

Short-lived peace talks between Khartoum and the rebels in Addis Ababa last April broke down over the issue of humanitarian access.

Thursday's dialogue "will be launched in a very different atmosphere" as the government now accepts the need for a comprehensive solution to Sudan's economic and political crises, veteran columnist Mahjoub Mohamed Salih wrote this week in The Citizen.

In the western Darfur region, another ethnic minority rebellion has dragged on for 11 years.

Insurgents there have joined the rebels from Kordofan and Blue Nile in a "Revolutionary Front", fuelled by complaints of economic and political neglect of their far-flung regions by the Arab-dominated regime in Khartoum.

President Omar al-Bashir is wanted by the International Criminal Court for alleged war crimes in Darfur.

Analysts -- and the rebels themselves -- say the wars need to be addressed together, not as separate problems as has been the government's practice in the past.

SPLM-N spokesman Arnu Ngutulu Lodi told AFP that Sudan's regions have been marginalised by an "elite" in Khartoum.

"We need to go to (a) more meaningful comprehensive settlement," he said late Wednesday.

The Ethiopian talks come two weeks after Bashir appealed for a political and economic "renaissance," with peace as the top priority. He repeated an invitation he made over the past year for a broad political dialogue, including with the rebels.

But diplomats say there was also something new -- acknowledgement by Bashir of the country's ethnic diversity, even after the secession in 2011 of overwhelmingly non-Arab South Sudan.

Diplomats say the Addis Ababa talks signal recognition within Bashir's 25-year-old regime that its current course is unsustainable.

The talks could be the start of a much broader national dialogue, drawing in opposition parties and other groups, to address discontent in outlying regions and ease pressure on a sanctions-hit, indebted economy starved of hard currency since South Sudan broke away with much of the country's oil reserves.

"The government, especially after the recent speech of the president, recognises that the first step to achieve the goals of the national consensus is to heal the wounds of the war," the pro-government Sudan Vision wrote in a Wednesday editorial.

Lodi accused the government of continuing aerial bombardments on Monday and Tuesday in Buram and Rashad districts, killing one man.

"We don't bomb any civilian areas," army spokesman Sawarmi Khaled Saad told AFP, adding the military "will continue its job" until a ceasefire is reached.