A gunman is seen entering Iranian parliament building in a still image taken from close circuit television (CCTV), taken on June 7, 2017, in Tehran, Iran. (Reuters photo)

TEHRAN, June 8 (Xinhua) -- Iran's Intelligence Ministry on Thursday released the pictures and first names of five gunmen as Iran nationals and members of the Islamic State (IS) who attacked the Iranian parliament and Imam Khomeini's shrine on Wednesday.

According to the ministry's statement, the five attackers had left Iran and were engaged in the IS operations in Iraq's Mosul and Syria's Raqqa, Tasnim news agency reported.

In August 2016, the five gunmen had returned to Iran for a terrorist operation under the command of Abu Aysheh, a ranking commander of IS, with the purpose of carrying out operations in Iran's religious cities, the statement said.

They fled Iran after their cell was dismantled at the time and their ringleader, Abu Aysheh, was killed, it added.

On Wednesday, six assailants attacked Iran's parliament and Imam Khomeini mausoleum in capital Tehran, whereby at least 17 people died and 52 others injured.

All the six assailants involved in the attacks were killed. The IS has claimed responsibility for the attacks.