According to Iranian state TV, six rioters were killed during an attack on a police station in the town of Qahdarijan.
It says all were shot by hunting rifles. Protesters have complained mostly about economic problems and have also denounced Iran's clerical leadership.
The towns are all in Iran's central Isfahan province, some 215 miles south of Tehran.
The protests are widely described as the largest since 2009, when demonstrators took to the streets to following the disputed re-election of President Mahmoud Ahmadinejad.
The state broadcaster said two others died in the western town of Dorud when they were hit by a fire engine stolen by protesters, and ILNA reported a school for clergy and government buildings were burnt in the north-western town of Takestan.
In the country's second-largest city of Mashhad, where demonstrations first kicked off on Thursday in protest against a surge in the prices of basic food supplies, activists said that it has turned into a large military base.
That brings the estimated death toll to 21 in five days of unrest that represent the biggest challenge to the Islamic regime since mass demonstrations in 2009.
In separate comments in a gathering of lawmakers on Monday, President Hassan Rouhani lashed out at his U.S. counterpart for commenting on the recent protests in Iran, saying the man who already called the Iranian people terrorists has no right to sympathize with the nation.
Authorities have also blocked access to Instagram and the messaging app Telegram to try to damp down the protests.
Iranian officials maintain that people have the right to stage protests to express their opinions, as long as the rallies comply with the legal conditions. They are hungry for food & for freedom.
He warned that Iran will use its right to reciprocate the enemies' hostile moves in a way that they will regret their deeds.
Previously, Germany called on both Iranian authorities and the protesters to restrain from violence. But there's only ONE way to change Iran: from inside, by the Iranian people.
"It's clear there's a kind of discontent that's sweeping Iran over broad issues".
Rouhani, a moderate force among Iranian hardliners, came to power in 2013 promising to mend the economy and ease social tensions, but high living costs and a 12 percent unemployment rate have left many feeling that progress is too slow.
Iran's intelligence ministry released a statement saying "instigators" have been identified "and will be dealt with seriously soon".