The group’s deputy leader, Abdul Rahim Dagalo, who is under American sanctions, was greeted by hundreds of cheering people as he arrived at the elaborate event, held at a state-owned convention center in downtown Nairobi.

Mr. Dagalo did not speak at the event, and a promised charter meant to pave the way for a parallel government in R.S.F.-controlled areas was not signed. Officials said they needed another three days to negotiate the terms of the charter with Abdel Aziz al-Hilu, the leader of another Sudanese rebel faction, who sat beside Mr. Dagalo.