Twenty-six alleged members of the Islamic State group went on trial in Iran on Saturday over attacks last year on parliament and the tomb of revolutionary leader Ruhollah Khomeini, local media reported.
Seventeen people were killed and dozens injured in the simultaneous attacks in Tehran on June 7 -- the first claimed by IS inside Iran.
The judiciary-linked Mizan news agency said several of the accused were Iranians who had left to join IS in neighbouring countries and returned for the attacks.
Five attackers were killed on the day, but police said at the time that five people had been arrested at the scenes of the attacks in central and south Tehran.
Dozens more arrests were reported in the following months -- many in operations along the borders with Iraq and Turkey.
There were few details from the first day of the trial, which was held in the presence of the victims' families.
Most of Iran's population is Shiite, and therefore considered heretics by the Sunni jihadists of IS, who have increasingly called for attacks on the country.
Iran has also supported the governments of Iraq and Syria against IS and other jihadist insurgents.