A series of earthquakes with a magnitude of at least 5 have hit the Iran-Iraq border and even rattled Baghdad and parts of the Iraqi countryside, striking in the same area that saw a tremor in November that killed more than 530 people.
The US Geological Survey said seven quakes struck near the Iraqi city of Mandali and an eighth struck near Mehran in western Iran.
There were no immediate reports of injuries or damage.
Seven had a preliminary magnitude of at least 5, while the eighth was a magnitude 4.
Earthquakes of magnitude 5 to 5.9 are classified as moderate, and can cause considerable damage.
Iranian authorities offered similar figures for the earthquakes on state television.
Online reports said people rushed into the streets as the tremors hit. In Baghdad, people felt a quake shake the Iraqi capital, followed by what felt like aftershocks.
All the earthquakes struck at a depth of six miles, according to the USGS.
The tremors were very shallow, which causes more ground shaking and potential damage, particularly in places without strict building codes.
In November, a major 7.2-magnitude earthquake struck the same region, killing more than 530 people and injuring thousands in Iran alone.
In Iraq, nine people were killed and 550 injured in the northern Kurdish region, according to the UN.
Randy Baldwin, a geophysicist with the USGS National Earthquake Information Centre in Colorado, said the quakes appeared to be aftershocks from the November tremor.
The area is in the sparsely populated and remote Zagros Mountains that divide Iraq and Iran and is home to many shallow faults, he said.
"It's ongoing activity there. If there was a stressed fault that's ready to move, they happen like that until the stresses are relieved, so it's not too unusual."
Iran sits on major fault lines and is prone to near-daily earthquakes. In 2003, a 6.6-magnitude quake flattened the historic city of Bam, killing 26,000 people.
Earlier on Thursday, the USGS said a magnitude-4.9 quake hit Iran's southern province of Kerman before dawn.
The official IRNA news agency said the tremor rocked the village of Hojedk, 400 miles south of Tehran, and struck at a depth of 6.2 miles. No injuries or damage were reported.
Kerman has also recently seen several quakes, ranging in magnitude from 4 to 6.2.