At least 10 people died and another 10 were injured Tuesday morning in a serious traffic accident in the Penza region, regional police said.
A minibus carrying 18 passengers collided with a Toyota off-road vehicle and then hit a large truck, but police have so far been unable to give the exact cause of the crash, Interfax reported.
The police are considering different versions of events, the mostly likely being that the minibus driver performed a dangerous overtaking maneuver, pulling out into oncoming traffic and colliding with a vehicle moving in the opposite direction, the report said.
However, police have not ruled out the possibility that the accident was caused by the minibus driver falling asleep behind the wheel and losing control of the vehicle.
"According to preliminary reports, the minibus driver was tired, could not stay alert and may have fallen asleep, which could have caused the accident," a police source said.
The large number of casualties may also have resulted from a collision with a third vehicle -- a Freightliner truck.
There were conflicting information about the identifies of the dead. Regional police said in a statement that the passengers were Tajik nationals traveling from Sochi to work in Chuvashia. But the Emergency Situations Ministry told Interfax that the dead passengers were residents of Chuvashia and the minivan's owner, also from Chuvashia, had died as well.
Earlier, police reported that 11 people had died, but one of the people previously presumed dead started to show "signs of life," Interfax said.
Police were working at the scene of the incident to determine exactly what happened.