DNEPROPETROVSK, Ukraine — Residents of this city held what they called a “unity rally” on Saturday meant to help mend a rift between President Petro O. Poroshenko and the regional governor he fired and ease worries that Ukraine, on top of everything else, is also now at risk of unraveling into privately ruled fiefs.

The country seemed to be teetering in that direction last week, when Mr. Poroshenko dismissed Igor V. Kolomoisky, the billionaire governor of Dnepropetrovsk, an important industrial region in the east, apparently for sending armed loyalists to Kiev, the capital, to occupy the offices of two state-owned energy companies that are central to a business dispute.

Mr. Kolomoisky had been one of the government’s staunchest allies, and his militias had helped stop pro-Russian fighters from moving beyond the eastern regions of Donetsk and Luhansk, where the pro-Russian fighters have been waging war for nearly a year.

But recently, Mr. Kolomoisky had clashed with the government over the future of the energy companies, in which he owned a minority stake.