The EU will impose new sanctions on 37 Iranian officials and organisations over the crackdown on protests, but is still debating listing the Revolutionary Guard as a "terrorist" group, diplomats said.
Foreign ministers from the bloc are to agree to adopt the fourth package of sanctions on Tehran over its repression of demonstrators at an already-scheduled meeting in Brussels on Monday.
Demonstrations have swept Iran since the death on 16 September, of Iranian Kurdish woman Mahsa Amini, 22, after her arrest in Tehran for allegedly failing to adhere to the Islamic republic's strict dress rules.
Iran has arrested at least 14,000 people in the wave of protests, according to the United Nations.
Authorities have executed four people for their role in the unrest and imposed the death penalty on a total of 18, triggering widespread international outrage.
The EU has already imposed asset freezes and visa bans on more than 60 Iranian officials and entities over the crackdown on protestors, including targeting Tehran's "morality police", Revolutionary Guard Corps commanders and state media.
But the 27-nation EU has so far stopped short of blacklisting the Revolutionary Guard itself as a terror group despite calls from Germany and other member states to take the step.
Iran has warned the bloc against taking the move and EU officials are wary that it could kill off stalled attempts to revive the 2015 deal on Tehran's nuclear programme being mediated by Brussels.
"I think it's not a good idea because it prevents you from going ahead in other issues," a senior EU official said.