The unrest that has swept Iran over the past six days will not help Italian companies invest in the oil-rich country, a top official from Italy's main business lobby Confindustria said on Tuesday.

"We need to see how the currently extremely difficult and highly critical situation evolves inside Iran," Licia Mattioli, Confindustria's Vice President for internationalisation, told AKI.

Many Italian companies have inked "large numbers of contracts" in Iran since it ended its trading isolation in 2016 after a deal with world powers to end crippling sanctions in exchange for curbing its nuclear activities.

These contracts - worth billions of euros - are currently "at different stages," said Mattioli.

"A country undergoing internal upheaval presents a complicated situation that can jeopardise such accords," she said.

But it would be "premature" to predict how current events will impact Italian companies and the contracts they have signed with Iran, she stated.

"But a country's stability is a necessary condition for foreign investment and is good for business," Mattioli said.

Officials say over 20 people have been killed and hundreds arrested in Iran since the protests broke out on Thursday in the northeastern city of Mashhad - and spread to the capital Tehran and several other provinces.

The unrest was ignited by frustration at Iran's sluggish economy but has widened to include open defiance of Iran's ruling clergy.