Interfax quotes an unnamed space official as saying that the capsule entered the atmosphere improperly, with the hatch first, instead of with heat shields leading the way.
The official says the hatch suffered significant damage.
The official also says the capsule's antenna burned up during the descent, meaning the crew could not communicate properly.
Space officials could not be immediately reached for comment on Tuesday's report.
The crew, which included South Korea's first astronaut, endured severe gravitational forces because it took a steeper-than-usual trajectory.