Security forces in Iran are cracking down on protests that spread across the country last week, after cuts to food and fuel subsidies caused prices to rise by as much as 300 per cent.
Senior police official Qasem Rezai warned that “illegal gatherings are intolerable and will be confronted”, reported Iran's semi-official ILNA news agency.
Social media posts showed tear gas being fired to disperse demonstrations on Thursday.
Non-governmental organisation Human Rights Watch said a “sociologist and four labour rights defenders” were among activists detained by the authorities.
The comes amid continuing protests led by the Co-ordinating Council of Teachers Syndicates to demand better salaries and pension plans.
Iranian authorities have blamed foreign activists for some of the dissent.
The Ministry of Intelligence said it arrested two Europeans intending “to abuse the demands of unions and other groups in society”.
The semi-official Mehr News agency reported last week that Iranian sociologist and activist Saeed Madani was among those arrested.
He previously spent at least five years in prison for “assembly and collusion against the national security” and spreading “propaganda against the state”, Human Rights Watch said.
US sanctions on Tehran have hurt Iran’s economy and humanitarian situation, affecting exports, banks, medicine and food production, Alena Douhan the UN special rapporteur on the impact of unilateral sanctions, said on Wednesday.
Former US president Donald Trump took his country out of the nuclear deal between Iran and world powers in 2018, citing Iran's continued missile development and regional meddling.
He re-imposed US sanctions lifted under the deal and introduced new, tougher measures against Iran.
Iranian anti-government activists and human rights groups accuse Tehran of diverting the country's resources to fund proxies across the region.