The body of the fourth person killed in the fireworks blast at the Avangard factory outside St. Petersburg has been found under the rubble.
"The fourth deceased has been found," to official said.
Earlier, local officials announced three victims of the blast.
"A third body has been found. It's a male," to official said.
READ MORE: Explosion at Mine in Russia's Rostov Kills One, Injures 5 — Emergency Services
Russian Investigating Committee said that blast was caused by violations of technological procedure and safety measures. The committee added that the main engineer of the Avangard factory was detained in the wake of the deadly fireworks blast at the facility.
"The main engineer of the Gatchina Avangard Factory has been detained on suspicions of committing this crime," the statement read.
The official is suspected of allowing unidentified unauthorized individuals to access the facility, according to the statement. These individuals were not employees of the factory and were not licensed for performing works at it, the statement noted.
"As a result of it, these individuals violated technological procedures and safety measures at the explosion-prone facility, leading to the blast," the statement added.
The explosion occurred earlier in the day at the Avangard fireworks factory in the Gatchina district of the Leningrad region. According to earlier reports by local emergencies services, the entire four-floor building collapsed and at least two people were killed, while several others could still be under the rubble.