Tasnim� A helicopter that crashed in the Caspian Sea early Sunday was a Mil Mi-17 chopper in possession of the Islamic Revolution Guards Corps (IRGC) Aerospace Force, and four of the five victims were servicemen, IRGC spokesman announced.

According to Head of the IRGC Public Relations Department General Ramezan Sharif, the IRGC helicopter was at disposal of Khazar Exploration and Production Company (KEPCO), a subsidiary of the National Iranian Oil Company (NIOC).

The aircraft was dispatched to Amir-Kabir semi-submersible drilling rig in the Caspian Sea, 20 kilometers off the port of Amirabad, at around 4:30 a.m. local time, to rescue an employee suffering a heart attack, Sharif explained.

After picking up the individual, the helicopter began to fly back to shore, but crashed shortly after take-off and descended into the sea, killing all five people on board, he said.

The oil company�s worker and four IRGC servicemen, all colonels, lost their lives in the crash, he noted.

The general said the cause of the incident is under investigation.

Amir-Kabir is the first Iranian facility for the extraction of oil and gas from the Caspian Sea.