GENEVA (Reuters) - A senior U.N. official said on Friday that talks on a ceasefire for Sudan would resume in the next day or two and described a change in the warring sides' stance which could make them more inclined to respect any future deal.

Sudan's military factions committed late on Thursday to a limited agreement to protect civilians and allow humanitarian aid after a week of talks in Saudi Arabia, but there was no commitment to peace and fighting continued on Friday.

Volker Perthes, U.N. Special Representative for Sudan, said he had spoken with one of the sides since and was assured of their willingness to keep talking.

"We expect these talks on a ceasefire to start off again from today or from tomorrow. It shouldn't technically take too long to agree on the modalities of ceasefire," he told a Geneva press briefing from Port Sudan.

Battles between Sudan's army and rival paramilitary forces have killed hundreds and wounded thousands, disrupted aid supplies, sent refugees fleeing abroad and turned residential areas of Khartoum into war zones since mid-April.

Past ceasefires have not held because both sides still felt they could win, he added, noting that he had since observed a change in the parties' stance.

"Both sides have realised that even if they win, it will not be a quick win. And that a dragged out, long war could damage the entire country and then there will not be too much to win," he said.

"You could lose the country, even if you win the battle."

(Reporting by Emma Farge; editing by Matthias Williams, William Maclean)