Iran's official IRNA news agency says that an air ambulance helicopter has crashed in southern Iran, killing all seven onboard.

The report Friday says the helicopter was carrying a patient in a serious condition from a remote area to the southern city of Shiraz when it crashed. Four helicopter medics were among the victims.

It says that the cause of the crash is not immediately known, but an investigation is underway.

Air accidents are not uncommon in Iran, and are often thought to be caused by aging aircraft and poor maintenance. Southern Iran has experienced wind, heavy rainfall and low visibility in recent days.