Iran has arrested the family of a young man killed during last month's protests, which were triggered by a significant rise in the price of gasoline and spread to more than 100 cities and towns.

The family of Pouya Bakhtiari had been invited for talks with the authorities, the semiofficial Mehr news agency said on December 24, citing what it called an informed source.

They were found to have been involved in a "counterrevolutionary project" and "anti-structural activities," according to the news agency.

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

Bakhtiari's parents had announced that they will hold a mourning ceremony at a cemetery in the city of Karaj, west of Tehran, on December 26 to mark 40 days since his death. They had invited Iranians to attend the event.

A relative told RFE/RL’s Radio Farda that Bakhtiari’s parents, as well as several other family members including his grandmother had been arrested by security forces.

Their whereabouts are unknown.

U.S. Secretary of State Mike Pompeo condemned the reported arrest of Bakhtiari's parents and called for their "immediate release."

"It’s time for the international community to stand together with the Iranian people and hold the regime accountable," Pompeo said on Twitter on December 24.

The 27-year-old Bakhtiari was reportedly killed in Karaj in antiestablishment protests that erupted in mid-November over a decision to hike gasoline prices by as much as 200 percent.

Bakhtiari’s father had said in media interviews that authorities had summoned him and told him to hold the ceremony in a mosque, citing concern it could create unrest. But he said he had refused to do so, saying he needed a larger space.

Officials in Iran have failed to issue a death toll for the deadly unrest while dismissing figures by international rights groups and others as exaggerated.

Amnesty International has said that at least 304 people were killed in the state crackdown on the protests.

Internet access was shut down all over the country for days at the height of the unrest, but images were smuggled out of fatalities and scenes of violence.

Iranian officials have blamed "thugs" connected to enemies abroad and the United States, Israel, and Saudi Arabia of involvement in the protests.

Meanwhile on December 24, witnesses reported a high security presence in the streets of the Iranian capital Tehran.

With reporting by Mehr, RFE/RL’s Radio Farda, AFP, and the BBC