Iranian students scuffle with police at the University of Tehran during a demonstration driven by anger over economic problems, in the capital Tehran on December 30, 2017.

Iran's army chief said on Thursday police forces had already quelled anti-government unrest that has killed 21 people but that his troops were ready to intervene if needed, official media reported, as new state-sponsored pro-government rallies were held.

The anti-government demonstrations, which seem to be spontaneous and without a clear leader, erupted a week ago in Iran's second city of Mashhad over economic hardships — mostly youth unemployment and alleged corruption.

"Although this blind sedition was so small that a portion of the police force was able to nip it in the bud ... you can rest assured that your comrades in the Islamic Republic's army would be ready to confront the dupes of the Great Satan (United States)," Major General Abdolrahim Mousavi was quoted as saying.

As the unrest spread across the country, protesters saying they were tired of anti-Western slogans and that it was time for both the clerical leadership and the government of President Hassan Rouhani to step down.

The demonstrators include members of the working class as well as educated Iranians from the middle class, which formed the backbone of pro-reform protests in 2009.

Following six days of demonstrations, the elite Revolutionary Guards Corps said on Wednesday that it had deployed forces to quell unrest in three provinces where most of the trouble had occurred.

That was the clearest sign yet that authorities were taking the protests seriously.

The Revolutionary Guards, the sword and shield of Iran's Shi'ite theocracy, were instrumental in suppressing an uprising over alleged election fraud in 2009 in which dozens were killed.