The US Geological Survey said the quake's epicentre was about 150km south of the city of Gorgan, at a depth of 10 km.

Tremors were also felt in the capital, Tehran.

Iran is criss-crossed by fault lines and experiences earthquakes regularly.

In 2003, an earthquake flattened the desert city of Bam and killed 31,000 people, about a quarter of its population.