European envoys withdrew from an Iranian business forum as tension rises over the execution of dissident Iranian journalist Rouhollah Zam.
Iran’s Foreign Ministry summoned the ambassadors of Germany, which holds the rotating EU presidency, and France after they denounced the death sentence.
France said the hanging was barbaric and unacceptable, and contrary to Tehran's international obligations.
The journalist was based in Paris before he was captured in Iraq and taken to Iran.
France said on Sunday that its ambassador to Iran would not take part in an online business forum in Tehran this week.
Envoys from Germany, Austria and Italy cancelled their involvement in the December 14 event, the French Foreign Ministry said on Twitter.
At the end of its tweet, the ministry ran the hashtag #nobusinessasusual.
Jake Sullivan, US president-elect Joe Biden's national security adviser, tweeted his dismay at the execution and what he called a horrifying human rights violation.
Organisers of the Europe-Iran business forum said they were postponing the event.
Zam was hanged on Saturday after Iran's Supreme Court upheld a death sentence passed in June for his role in protests during the winter of 2017-2018, among other charges.
At least 25 people were killed during the unrest in December 2017 and January 2018 that was sparked by economic hardship.
The journalist's father, Mohammad Zam, a cleric who served in high-ranking government positions in the 1980s, said he met his son a day before his execution, which the condemned man was not told had been confirmed.
He was executed four days after the Supreme Court ruling. Amnesty International said that was aimed at pre-empting an international campaign to save Zam's life.
Mr Zam said that after the arrest, his son was not allowed to see family or lawyers for nine months and was permitted to meet only a court-appointed lawyer under the supervision of security personnel.
His claims were reported by Amnesty International.
Also on Sunday, Iranian media reported the sentencing of Kameel Ahmady, an ethnic Kurd British-Iranian anthropologist, to nine years in prison for subversive research.
His work included studies on child marriage and female genital mutilation.