USGS said the quake was at a depth of 65 kilometers (40 miles) and struck 114 km northwest of the city of Ilam, close to Iran's border with Iraq.
The Iraqi Geological Survey said the quake had been felt in the capital Baghdad and in Erbil in the Kurdistan region.
"About 200 to 210 people have been injured ... but we have had no fatalities," Houshang Bazvand, the governor of Kermanshah province, told state TV.
"No reports of any fatalities (have been reported) yet and most of the injured were hurt while fleeing, not due to quake damage," Pirhossein Koulivand, head of the Iranian emergency services, told state TV.
Fears of aftershocks sent people in several cities in the western province of Kermanshah out onto the streets and parks in cold weather, Iranian media reported.
Six rescue teams were immediately deployed to the quake-hit area and some 100 people had been slightly injured, Iranian TV said.
The quake also triggered landslides but officials said all the roads in the area remained open to traffic and electricity had been restored in most of the quake-hit areas.
Iranian media said the quake was felt in at least seven provinces of Iran and was strongest in Kermanshah province, where last year over 600 people were killed and thousands injured in Iran’s deadliest earthquake in more than a decade.
Fifty people were injured in Sarpol-e Zahab, about 15 km (10 miles) from the border, near the epicenter of the quake, and 50 in another town nearby, Houshang Bazvand, the governor of Kermanshah province, told state TV.
The quake was felt in some areas of Kuwait but no damage was reported, state news agency Kuna said.
"Fortunately, the quake was not near bigger cities. But it might have caused damage in villages and I hope not that many villages are located where it hit," Ali Moradi, head of Iran's seismology center, told state TV.
Iran sits astride major fault lines and is prone to frequent tremors. Last November, a magnitude 7.3 earthquake hit the Kermanshah province. In 2003, a quake of a magnitude of 6.6 in Kerman province killed 31,000 people and flattened the historic city of Bam.