Five people on board an Iranian helicopter were killed when it crashed into the Caspian Sea on Sunday, state television reported.
The bodies of four crew and a civilian, plus the helicopter, had been found, a security official told state television website.
The helicopter, owned by the National Iranian Drilling Company, was carrying an emergency patient from Amir Kabir offshore oil platform when it "disappeared half a mile from the oil rig on its way back," ISNA news agency quoted Behshahr governor Khalegh Sajadi as saying.
"The reason of the crash will not be known until the black box is found," he added.
Amir Kabir drilling rig is 137 air miles (250 kilometres) off the Caspian Sea coastal line and extracts oil from the water depth of 1,000 metres, according to official IRNA news agency.