The rebuke, issued by Sweden days after assuming the EU's rotating six-month presidency, comes as the 27-nation bloc searches for a unified response to Tehran following its post-election crackdown and detention of British embassy staff.
"The Presidency strongly condemns the executions in Iran during the past few days, in particular the execution of 20 persons in Iran on 4 July," Sweden said in the statement, adding Iran should abolish the death penalty entirely.
Prior to Saturday's hangings, Iranian media reported last week that six drug traffickers were executed in a prison in Qom and six people were hanged for murder in Tehran.
On Friday, EU countries summoned Iranian ambassadors to protest the detention of British embassy employees, and are mulling tougher measures in future such as visa bans and the withdrawal of EU ambassadors from Iran.
Of the nine British embassy staff detained and accused of inciting the street protests in Iran, one remains in custody and one was set to be released on Sunday.
While the EU has led the international outcry over Tehran's crackdown on demonstrators protesting Mahmoud Ahmadinejad's victory in the June 12 presidential elections, some of the bloc's members fear going too far and derailing talks on Iran's nuclear program.
French President Nicolas Sarkozy has called for harsher sanctions against Iran, but analysts say Germany and Italy are among those skeptical.
(Reporting by Anne Jolis; Editing by Jon Hemming)
