Riot police and security forces clashed with demonstrators in Tehran and dozens of cities across Iran on Saturday, Iranian news agencies said, as protests against a rise in petrol prices turned political.

The reports said demonstrators chanted anti-government slogans around the country, a day after the government increased the price of regular petrol by fifty percent and rationed it.

State television said police clashed with what it called rioters in some cities and fired teargas to disperse them.

One person was killed and several people were wounded in the city of Sirjan in Kerman province on Friday, the ISNA news agency quoted a local official as saying on Saturday.

"People attacked a fuel storage warehouse in Sirjan and tried to set fire to it", the state news agency IRNA said.

Protests spread to at least 40 cities and towns on Saturday, Iranian media said.

Videos posted on social media from inside Iran showed protesters setting fire to buildings and clashing with riot police. In other videos, protesters blocked roads and set fires in the streets in Tehran and some other cities. Some chanted slogans against top officials.

Video footage also showed riot police firing teargas and using clubs to disperse protesters. A video shared on Twitter showed protesters setting fire to a bank.

State-run TV accused "hostile media" of trying to exaggerate the size of demonstrations by "using fake news and videos on social media".

General Prosecutor Mohammad Jafar Montazeri told state TV that demonstrators who blocked roads and clashed with security forces "certainly have roots outside the country".

Protesters were seeing slower internet speeds and limited access, social media reports said, an apparent effort by the authorities to limit communication between protesters.

Many people in oil-producing Iran see cheap petrol as a national right and price hike sparked worries about a further squeeze on living costs, despite assurances from the Iranian authorities that the revenue raised would be used to help needy families.

People's struggle to make ends meet has worsened since last year, when the United States pulled out of Iran's 2015 nuclear deal with six powers and reimposed sanctions on the country.

Combined with rising inflation, growing unemployment, a slump in the rial and state corruption, Washington's policy of "maximum pressure" has further crippled the economy.

The clerical rulers are anxious to prevent any repeat of unrest in late 2017, when people staged protests in 80 cities and towns over poor living standards, some calling on Shi'ite Muslim clerical leaders to step down. Iranian officials said 22 people died in those protests.

Lawmakers will debate the price hike decision on Sunday, Iranian media reported, adding that some of them are urgently preparing a motion aimed at forcing the establishment to revise its decision.

Iranians mainly rely on cars or taxis for access around cities and towns. The government said the cost of using taxis and public transport will not change, according to media reports.

The petrol price increase is expected to raise around 2.25 billion euros a year for additional subsidies for 18 million families, or about 60 million Iranians on lower incomes, the government said.