News reports say an Iranian helicopter based at a Caspian Sea oil platform crashed late on November 26, killing all five people onboard.
The helicopter belonged to the Oil Ministry and was carrying an engineer with heart trouble to the hospital when it crashed, the German news agency dpa reported, citing Iranian media.
The cause was not immediately clear.
By November 27, the bodies of three of the victims had been recovered, reports said.
The helicopter crash came one day after a train wreck in northern Iran killed at least 44 people.