The blast, which occurred on Friday outside the regional capital of Makhachkala, also injured 23 people, it said.
Healthcare minister aide Alexei Kuznetsov said that four people remained in hospitals, including one in serious condition, Russian state news agency RIA reported.
Dagenergo, the regional power operator, said on Friday that power supply was partially disrupted in nearby districts..
A local branch of the Investigative Committee, which deals with serious crimes in Russia, said it had opened a criminal case.
Preliminary results showed no traces of explosives at the scene, the committee wrote on Telegram.
Dagestan Governor Sergei Melikov told a briefing that some violations had previously been discovered during inspections of the petrol station but that these had been resolved before the blast, state agencies reported.
More than 130 petrol stations in Dagestan closed over the past year for various violations had resumed operations as a result of local court decisions, Melikov said.
The search operation after the blast is ongoing, he said.
Local authorities declared Sept. 28 a day of mourning in the region.
