Updated

The death toll from the partial collapse of a Russian apartment building rose to 38 Thursday after more bodies were discovered by crews searching a huge pile of concrete rubble for a fourth day.

Three people who lived in the fallen section of the 10-story building in the city of Magnitorgorsk remained unaccounted for, according to state news agencies. Officials think an explosion triggered by a gas leak caused the collapse.

The number of deaths stood at four for most of Monday, but climbed quickly after two nights of winter weather. Russian authorities acknowledged from the start that the extreme cold gave rescue crews less time to reach trapped survivors.

Hope flared when a 10-month-old boy was extracted from the wreckage alive on Tuesday. He was flown to a Moscow children's hospital for treatment. The baby suffered frostbite from lying in the rubble for 35 hours - temperatures were as low as minus 20 degrees Celsius (minus 4 F.)

State news channel Rossiya-24 cited doctors saying the child also had injuries indicative of "crush syndrome" - major shock and kidney malfunction characteristic of people trapped under heavy objects. His condition was assessed as serious but stable, the Russia Health Ministry said Wednesday.

On Thursday, the mayor of Magnitorgorsk told journalists there was no connection between the explosion at the apartment building and the fiery explosion of a minibus on the same street a day later.

The vehicle explosion took place about 2.5 kilometers (1.5 miles) from the apartment block. Police said the minibus was carrying gas canisters but have given few other details.

But video of the burning vehicle, including some posted on YouTube by Russia's RT satellite TV channel, featured sounds resembling gunfire and an observer's voice is heard saying people are shooting assault rifles.

Unconfirmed reports have suggested the apartment blast could have been a terrorist act and that the occupants of the exploded vehicle were suspects.

"I want to say that there are no clear facts showing any kind of confirmation of what is described on the internet today," Mayor Sergei Berdnikov said of the reports, according to state news agency Tass.