The authorities have opened an investigation into the fire which broke out on August 21 in the center of the southwestern Russian city of Rostov-on-Don, the press service of the Interior Ministry said in a statement quoted by Russian news agencies.
"A team of investigators has been working on the site of the fire," the statement said.
"Investigators are currently looking into various possible causes of the fire, including human error and technological malfunction," the statement added.
According to the emergency services, the fire damaged around 100 buildings in downtown Rostov-on-Don, but there were no fatalities.
The region's health minister, Tatyana Bykovskaya, said 36 people were injured in the fire.
Medical sources earlier said that 45 people had been injured, seven of whom had been taken to the hospital.
A state of emergency had been declared in the city and its surroundings, Russian Emergency Situations Minister Vladimir Puchkov said.
"We're declaring a state-of-emergency situation on the entire territory of the Rostov region. It's an emergency situation at the federal level," Puchkov said in Moscow.