Taha Osman al-Hussein, a former aide to Mr. al-Bashir, fled Sudan to Saudi Arabia in 2017 amid accusations he was a Saudi intelligence asset. A month later, he was appointed to the Saudi royal court as an adviser on African affairs.

Last week, according to several western officials, Mr. al-Hussein returned to Khartoum, stoking suspicions among protesters who denounced him in posters that he had come to do covert work on behalf of the kingdom.

Talks between Sudan’s protesters, led by the Sudanese Professionals Association, and the military, resumed on Wednesday after stalling briefly. Bankers and senior judges have joined the sit-in, strengthening the hand of the protesters. In recent days, both military and protest leaders have spoken positively about the possibility of a power-sharing council to run Sudan before elections set to take place up to two years from now.

But the key question, of whether a military general or civilian leader would hold ultimate power during that period, is unresolved. Protest leaders still hope they can get the Saudis and Emiratis on their side.

“I advise them to link with the real representatives of the people of Sudan, and not to make a deal with any party that is not connected to the people,” said Mohamed Yousif, a university professor and protest leader. “If the people see an attempt to impose something that runs counter to their interests, they might rise up again.”