The interior minister warned protesters will "pay the price" as footage on social media showed thousands marching across the country overnight in the biggest test for the Islamic republic since mass demonstrations in 2009.

The spate of demonstrations began in second city Mashhad on Thursday over high living costs, but quickly spread throughout the country and turned against the Islamic system as a whole, with slogans such as "Death to the dictator".

Lorestan province deputy governor Habibollah Khojastehpour told state television that two people were killed in clashes in the small western town of Dorud late on Saturday, but denied security forces were responsible.

There were no signs of major protests during the day on Sunday, though officials appeared to be bracing for unrest after dark.