Iran's President Hassan Rouhani called Wednesday for the release of innocent people who were arrested during nationwide protests against a fuel price hike last month.

Demonstrations erupted in Iran on November 15 against the unexpected decision to raise the price of petrol by as much as 200 percent.

Iran has yet to give overall figures for the number of people arrested when security forces moved in to quell the unrest that saw buildings torched and shops looted.

"All those people who have been arrested, of course some of them are innocent and should be freed," Rouhani said in an address broadcast by state television.

"There are some who... have committed an offence, not a crime. Someone has set fire to a tyre; we must not keep them for what they've done.

"What they've done was not right but... we must not be strict with these people," he said.

But Rouhani said people who used weapons or committed serious crimes during the violence should be treated separately.

"Those who are criminals must be dealt with according to the law," he said.

They included "those who have come to this incident in an organised manner", he added.

Rouhani said their "confessions" would be broadcast "in the future, and you will see they had been planning for more than two years".

"Their masters abroad told them that now is the time, carry it out... these people must be dealt with."

Iran has blamed the violence that broke out on "thugs" backed by its arch-foes the United States, Israel and Saudi Arabia.

It has also accused exiled royalists and the People's Mujahedeen of Iran (MEK), an exiled former rebel group which it considers a "terrorist" cult, of being behind the violence.

Authorities have yet to issue overall figures for the number of people killed in the violence.

London-based rights group Amnesty International said on Monday that at least 208 died, but Iran has dismissed such reports as "utter lies".

Israel