Russia's top investigative agency says that at least six people have died when a bus fell off a mountain road in Crimea.

The Investigative Committee's branch in Crimea said that the bus traveling from Sudak to Kerch veered off the road and fell 50 meters (164 feet) into a ravine Thursday. It said four passengers, including a child, died on the spot and another two later died in a hospital.

Investigators said that there were 19 passengers and a driver on the bus, and all survivors have remained in grave condition. Investigators opened a probe into possible violation of safety rules.

Russia annexed Crimea from Ukraine in 2014 following a hastily called referendum.