Quake injures more than 30 in southwest Iran
The quake struck at 10:05 pm (1835 GMT) near the town of Sisakht, in a mountainous district of Kohgilouyeh and Boyer-Ahmad province, the US Geological Survey said.
It left 32 people injured, two of them seriously, and caused "extensive damage to buildings, infrastructure and homes", Iran's state news agency IRNA reported.
According to a preliminary survey, "78 villages suffered serious damage with some houses completely destroyed", it said.
The magnitude of the quake was sufficiently large that most villagers spent the night out in the open for fear of aftershocks, it added.
Iran sits astride the boundaries of several major tectonic plates and experiences frequent seismic activity.
In June, a quake near Mount Damavand, Iran's highest peak, killed one person and injured more than 20 just east of the capital Tehran.
Last February, a 5.7 magnitude earthquake that rattled the western village of Habash-e Olya killed at least nine people over the border in neighbouring Turkey.
Iran's deadliest quake was a 7.4-magnitude tremor in 1990 that killed 40,000 people in the north of the country, injured 300,000 and left half a million homeless.