Iran has arrested the family of a young man killed in street violence that flared during last month's protests against fuel price hikes, Mehr news agency reported on Tuesday.

The family of Pouya Bakhtiari, who was "killed suspiciously during the recent riots", had been invited for talks with authorities, Mehr said, citing what it called an informed source.

They were found to have been "carrying out a counter-revolutionary project" and "anti-structural activities", said the agency, which is close to moderate conservatives in Iran.

"Consequently, these elements were arrested by a judicial order in order to protect the order and the security of the honourable people and others damaged by the rioters," it said without specifying which family members were taken into custody.

Bakhtiari was reportedly killed in Karaj city, west of Tehran, in street violence that erupted in mid-November during nationwide protests over a shock decision to hike petrol prices by as much as 200 per cent. He was 27.

His Instagram account, which is now reportedly run by his father, announced a ceremony marking 40 days since his death would be held at Karaj cemetery on Thursday.

It was still active with more than 18,000 followers on Tuesday.

Officials in Iran have yet to issue an overall death toll for the unrest, but international human rights group Amnesty International has put the number at more than 300.

An Iranian security official rejected a foreign media report on Monday that the figure was as high as 1,500, saying it was based on “false propaganda”.

"This way of news writing and making accusations is essentially nothing special," said Alireza Zarifian Yeganeh, head of the information and communications secretariat of Iran's Supreme National Security Council.

'Ludicrous claims'

Quoted by the Tasnim news agency, he dismissed the reports as "a series of ludicrous claims".

"And when you would ask this media about its source, it would refer to some invisible creatures and there is no possibility of verification."

The days of unrest in Iran from November 15 saw police stations attacked, shops looted and banks and petrol stations torched as authorities imposed a week-long internet blackout.

Videos that have surfaced since purport to show scenes from the crackdown that followed, including footage of security forces firing at unarmed demonstrators or beating them with batons.

The United States, France and Germany have all condemned Iran over the bloodshed.

Iran has repeatedly denied casualty figures issued abroad.

In a report on December 2, state television charged that foreign media had been "hyping up" the death toll.

It also said that security forces "had no choice but to resort to authoritative and tough confrontation in order to save people from the hands of the rioters, and a number of rioters were killed".