TEHRAN, Nov. 27 (Xinhua) -- Altogether five people were killed in a helicopter crash in the Caspian Sea in northern Iran on Sunday.

The accident happened at 04:20 a.m. local time (0050 GMT) as the helicopter, belonging to Iran's Oil Company, crashed near Amir Kabir drilling rig over the Caspian Sea, state IRIB TV reported.

Rescue workers pulled all five bodies out of the waters off the coast of Behshahr in the east of Mazandaran province, Press TV reported.

The helicopter was carrying a patient, a health worker and three crew members.

The black box has not been recovered yet, and investigation is underway for cause of the incident, the report said.