The cause of Thursday's early morning blaze in Makhachkala, 1,000 miles south of Moscow, appeared to be a short circuit, said Mirzabala Mirzabalayev, head investigator in the regional prosecutor's office.
The rescue efforts were hampered by the children's inability to hear shouts or the instructions of firefighters. Some of the boys hid under furniture in fear.
Mirzabalayev said prosecutors have opened an investigation for possible charges of negligence.
The Izvestia daily on Friday quoted fire officials as saying that the boarding school director had been cited for fire safety violations, including the lack of an alarm system, three times between November 2001 and August 2002. Alarm systems for the deaf or hearing-impaired can use visual warnings, such as lights, or vibrations.
The newspaper quoted the director, Raisa Magomedova, as saying that she didn't think such a system was necessary since the school had night attendants and a watchman. She accused the firefighters of having inadequate supplies of water and foam to fight the blaze.
Families across the Dagestan held funerals for 25 of the dead children on Friday, while other residents of the region observed a day of mourning, with flags lowered to half-staff and all entertainment programs canceled. Three of the dead have not yet been identified.
One of the most severely injured, Abdul Sultanov, was flown to Moscow on Friday for treatment, said Valentina Kostrova, Dagestan's chief pediatrician. The boy had burns over a quarter of his skin and suffered from burns on the respiratory tract, she said.
Three other critically injured children were on artificial respirators in Makhachkala hospitals, she said. Twenty children were in intensive care as of Friday.
The fire came three days after a blaze destroyed a wooden schoolhouse in the Siberian region of Yakutia, killing 22 students and injuring at least 10.
