The assailants who carried out the two deadly attacks in Tehran resulting in the deaths of 13 people were Iranians who were recruited by the Islamic State (IS) terror group, a top security official said on Thursday.
In an interview on state TV, Reza Seifollahi, deputy chief of Iran's Supreme National Security Council, said the attackers "had joined the IS from a number of regions inside Iran", reports the BBC.
"These people were cooperating with the IS in Syria and Iraq, and following the recent losses of the IS in both countries, they returned," Xinhua news agency quoted Seifollahi as saying.
The IS, a hardline Sunni jihadi group, claimed the attacks and threatened further assaults on Iranian Shia Muslims.
Suicide bombers attacked parliament and the mausoleum of the Islamic Republic's founder Ayatollah Khomeini on Wednesday.
The twin attacks were simultaneously carried out at around 10.30 a.m.
All the attackers were killed. Five people believed to be planning a third attack were arrested, officials said.
Forty-three people were also injured.
Iran's Revolutionary Guards had earlier accused Saudi Arabia and the US of being behind the attacks.
The violence comes amid heightened tension in the Middle East, with Saudi Arabia and other Arab states cutting ties with Qatar over alleged support for Islamist militants and closer ties with Iran.