The five men who carried out twin attacks in Tehran were Iranians who joined the Islamic State group in Iraq and Syria before returning last summer, the intelligence ministry said Thursday.
"The five known terrorists... after joining the Daesh (IS) terrorist group, left the country and participated in crimes carried out by this terrorist group in Mosul and Raqa," the ministry said in a statement.
The statement indicates only five people carried out Wednesday's twin attacks, rather than six originally reported.
The ministry released images and the first names of the dead attackers, who killed 17 people and wounded dozens in gun and bomb assaults on Tehran's parliamentary complex and the shrine of revolutionary founder Ayatollah Ruhollah Khomeini on Wednesday.
It said the five men were part of a network that entered Iran in July-August 2016 under the leadership of "high-ranking Daesh commander" Abu Aisha and that "intended to carry out terrorist operations in religious cities."
Abu Aisha was killed and the network forced to flee the country, the statement said. It was not clear when the five men returned to Iran ahead of Wednesday's attacks.