A magnitude 5.1 earthquake struck near Iran's Bushehr nuclear power plant on Friday, the US Geological Survey said.
The quake was moderate, which can cause considerable damage, and was centred 53 kilometres east of the plant on Iran's southern coast.
The USGS registered the quake, which struck at about 5.23am, at the relatively shallow depth of 38.3 kilometres, which would have amplified the shaking.
Iranian state media did not immediately report on the tremor and there were no immediate reports of damage or injuries.
Bushehr Nuclear Power Plant (BNPP) was Iran's first commercial nuclear reactor and remains its only nuclear power plant.
The plant was connected to the Iranian national grid in September 2011 and began producing power in 2013.
Russia and Iran began construction on a second reactor at the plant in November.
Iran is crossed by several major fault lines which cover around 90 per cent of its territory.
In early November, a magnitude 5.9 earthquake struck the country's north-west, killing at least five and wounding over 300 people.
In 2003, a 6.6 magnitude earthquake flattened the historic city of Bam, killing 26,000 people.
Though the plant is close to the city of Bam, it was not damaged in the 2003 quake.
The plant's location in Iran - one of the most seismically active regions in the world - has raised fears of a nuclear accident but it is designed to withstand strong earthquakes without sustaining serious damage.