Iran announced on Tuesday it would respond to EU and UK sanctions, vowing to target individuals and entities in the West that "violate human rights".
Tehran said it "strongly condemned" new sanctions imposed by Brussels and London in response to the regime's violent crackdown on protesters.
It warned retaliatory measures would soon follow.
"The Islamic Republic will soon announce a list of new sanctions against the human rights violators of EU and England," Iran's Foreign Ministry Spokesperson Nasser Kanaani said in a statement.
"The action of the European Union and the British regime is a sign of their mental inability to properly understand the realities of Iran," Kanaani was quoted as saying by the Iranian news agency IMNA.
"They are against the authorities of the Islamic Republic," he added.
At a meeting in Brussels, the EU slapped sanctions on more than 35 Iranian officials and organisations, blaming them for the "brutal" crackdown on unrest and other human rights abuses.
The list included four commanders and 12 units of the powerful Revolutionary Guards, who many observers say hold the real power inside Iran.
However, the bloc stopped short of placing the Guard on its list of terrorist organisations, despite a request from the European Parliament.
"A court decision is necessary" to start this process, said the EU's top diplomat Josep Borrell.
Brussels also invoked Tehran's supply of Iranian-made drones to Russia, which Moscow has used to cripple Ukraine's energy infrastructure.
The US and UK have issued new sanctions against Iran, reflecting a deterioration in the West's already dire relations with Tehran.
Tensions between London and Tehran spiked last week following the execution of the Iranian-British national Alireza Akbari in Iran for alleged "spying".
Observers have said that Akbari's hanging could indicate a power struggle within the regime, as he was part of a group that wanted authorities to give more concessions to protesters.
The sanctions are the latest response to Iran's deadly clampdown on unrest, sparked by the death of young Iranian Kurdish woman Mahsa Amini in police custody in September.
Four months after the start of anti-government unrest, the US-based Human Rights Activists News Agency says 516 protesters have been killed, including 70 children.
The latest figures from the group put the number of people arrested at more than 19,200, among them 687 students.
Systematic rape and sexual assault of female demonstrators have been reported in detention facilities across Iran.
The EU has already imposed an asset freeze, visa ban and ban on receiving EU funding on more than 60 Iranian officials and entities due to the regime's suppression of protests.
On December 12, Iran sanctioned the UK intelligence service MI5, UK military officials as well as German political figures in retaliation for previous sanctions.
French satirical magazine Charlie Hebdo and the Persian department of Radio Free Europe were also sanctioned by Tehran.