A court in Tehran has sentenced two Iraqis and one Iranian to prison over their participation as minors in a purported suicide mission planned by the Islamic State (IS) extremist group, according to the government-run Iran daily.

All were said to be part of a 21-member team that had crossed the Iraq-Iran border some three years ago to carry out the planned attack, which was not described in any detail.

Their sentences were handed down on September 6.

Reports on trials of alleged IS members in Iran are rare. The extremist group has regularly threatened Iran in the past.

The Iraqis, who were 14 and 17 at the time of their arrest, were each sentenced to five years in prison on the charge of "moharebeh," or waging war against God, which in Iran may be punished by death. They got additional one-year sentences for possessing weapons.

They will reportedly be handed over to Iraq's intelligence service.

The Iranian national was 16 at the time of this arrest, according to Iran daily, and was sentenced to five years in prison on similar charges.

The report says the three were not given the death penalty because they were under the age of 18 at the time of their arrest.

The report said that 16 members of the alleged IS team were arrested by Iranian forces while five others, including the leader of the group, were killed in clashes.

Three Iranian security troops were also killed in the clashes, it said.

Prosecutors reported jailing 16 female IS members in 2018 after their return from Syria.

At least 17 people were killed and dozens more wounded in twin 2017 attacks on Iran's parliament and the mausoleum of the founder of the Islamic republic, Ayatollah Ruhollah Khomeini, that were claimed by IS.