The United Nations 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.

"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," Ali Al-Za'tari, head of the UN mission in Sudan, said in a statement.

There are no figures for how many people have died in the Kordofan region and Blue Nile, where rebels have been fighting for nearly three years, but the UN says an estimated 1.2 million have been displaced or otherwise affected.

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

There has been no aid access into SPLM-N areas from within Sudan since 2011.

"Once agreement for a viable cessation of hostilities has been reached, the United Nations in Sudan stands ready to provide such assistance without delay," Za'tari said.

"And once peace is established full development efforts should be started immediately."

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

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