Sudan's warring rivals have agreed to send representatives for negotiations, potentially in Saudi Arabia, the United Nations' special representative in the country, Volker Perthes, said.

Mr Perthes told the Associated Press (AP) news agency on Monday that the talks would initially focus on establishing a “stable and reliable” ceasefire monitored by national and international observers.

He said the two sides had already named their representatives for preliminary discussions but cautioned that logistics for talks were still being worked out.

Mr Perthes also said that in the past week he had noticed a "change in tone" from the two warring sides, noting their realisation of how dangerous the situation had become and that any victory would be won at "too great a cost".

No definite information is available on the when and where of the negotiations. The UN official said both sides would have to agree on the venue.

The mediation efforts continued as the two sides clashed in the capital, Khartoum, despite another three-day extension of a fragile ceasefire.

Explosions and sounds of gunfire were reported in parts of Khartoum and its neighbouring city, Omdurman, on Monday.

The two sides announced late Sunday they would abide by a 72-hour extension of their nominal ceasefire of the past week.