He showed a scheme of an AS-28 deep-see vessel's stern entangled in a net, a hose and a rope to journalists.
Pepelyayev assumed that it could have happened when the vessel had been turning around despite the propeller's special protection.
At first, the submersible tried to free itself from the net but a hose and a rope wound around the propeller, he said.
Three Scorpion unmanned rescue vehicles delivered by U.S. and British plane will arrive at the site of the rescue operation in the afternoon, Pepelyayev said.
He said that it would take ships with the rescue vehicles onboard 3.5 hours to reach the rescue area. More time will be needed to discharge them from planes, deliver to the port and load into ships.
Cables are currently being attached to the submersible using the Tiger unmanned deep-sea vehicle, he added.
Pepelyayev also said: "We believe the crew has enough air supply till the end of the day and even more."