GENEVA, May 12 (Reuters) - A U.N. senior official expressed optimism on Friday that mediators would reach a ceasefire in the next few days, saying that he had assurances from one of the sides that they would continue negotiating in Saudi Arabia.

"I think the most important element of this understanding that was signed yesterday night is that both sides commit to continue their talks," Volker Perthes, Special Representative of the Secretary-General for Sudan, told journalists in Geneva, adding that he had spoken to one of them this morning. (Reporting by Emma Farge; editing by Matthias Williams)