An Iranian court has sentenced eight men to death in connection with terrorist attacks by the Islamic State (IS) extremist group that killed 18 people at the parliament and Ayatollah Ruhollah Khomeini's mausoleum.

The sentences were issued on May 13 by the Islamic Revolutionary Court in Tehran.

Eighteen other suspects still face charges over the attacks in June 2017 by suicide bombers and gunmen.

Iran has said the five gunmen and suicide bombers who were killed during the attack had previously fought in Syria and Iraq as part of the IS militant group.

Musa Ghazanfarabadi, the head of the Revolutionary Court, told state television that the death sentences could be appealed in the Supreme Court.

Ghazanfarabadi said the Revolutionary Court would also hear claims against the United States and Saudi Arabia that were filed by families of the victims of the attacks.

Iran's powerful Islamic Revolutionary Guards Corps accuses the United States and Saudi Arabia of being behind the IS action.

Washington and Saudi Arabia deny the accusation.

Based on reporting by Reuters, AP, and AFP