It is unclear where the mastermind was killed, although it is believed one of the attackers came from the Kurdistan region of Iran.
Ali Asghar Gorjizadeh, the commander of IRGC's Ansar-ol-Mahdi Corps, which is responsible for protection of senior Iranian officials, said in a televised interview on Saturday that from the very first moments after the twin terrorist attacks, members of the Ansar-ol-Mahdi Corps took measures to encounter the terrorists.
The attack last week was the worst terror atrocity faced by the country since 1981, when a bomb planted by an Iranian opposition group in Tehran killed 27 Iranian members of parliament and dozens of officials.
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Tuesday night's shooting is two blocks away from where 17-year-old Fabian Nunez was gunned down earlier that same day. Images from the scene showed a white tent over the front of a police cruiser that was stopped askew on the sidewalk.
Ali Larijani stressed that the Iranian Parliament will show a serious reaction to the recent US Senate bill that would impose new sanctions on Iran, calling on the national security commission to present a plan on countermeasure for the bill as soon as possible; "The US must realize that Iranian parliament has a strong resolve in the fight against terrorism", he added. The ISIS media wing, Amaq, claimed "fighters with the Islamic State" carried out the assault.
With the latest arrests, the number of people detained since June 7 in relation to the attacks in the capital or extremist cells has passed 50.
On Wednesday morning, terrorists launched simultaneous attacks on Iran's parliament building in downtown Tehran and on the mausoleum of Imam Khomeini, south of the city.
"The [terrorist attacks] indicated that the terrorist groups had failed to achieve their main goal and targeted the parliament and Imam Khomeini Mausoleum, finally resorted to martyring the innocent people and the staff at the parliament", Larijani added.
IS has claimed responsibility for this week's twin attack in Tehran.