Iran executed Swedish-Iranian dissident Habib Chaab for "terrorism" on Saturday, according to the judiciary.

"The death sentence for Habib Chaab... nicknamed Habib Asyud, the head of Harakat al-Nidal terrorist group... was executed today, Saturday morning," the judiciary's Mizan Online website reported.

Chaab had been held in Iran since October 2020 after he vanished during a visit to Turkey and was put on trial in Tehran.

Convicted of "corruption on earth" for heading a rebel group, he was sentenced to death on December 6.

Stockholm has denounced the decision as "inhumane".

According to Mizan Online, Chaab led Harakat al-Nidal, or the Arab Struggle Movement for the Liberation of Ahvaz, which Iran considers a "terrorist group" and blames for orchestrating attacks in southwestern Khuzestan.

The oil-rich province is home to a large Arab minority, and its people have long complained of marginalisation.

Iranian authorities accused Chaab of staging attacks since 2005 "under the protection of two spy services, including the Mossad and Sapo" -- Israeli and Swedish agencies, respectively.

According to the prosecution, other leaders of Harakat al-Nidal are based in Denmark, the Netherlands and Sweden, with the group receiving financial and logistical support from Saudi Arabia.

Iran executes more people yearly than any other nation except China, according to rights groups including Amnesty International.

Three dual nationals -- including Chaab -- have been sentenced to death or executed over security-related charges since the start of the year, according to the judiciary.

In January, Alireza Akbari, a former Iranian official with British citizenship who had been convicted of espionage, was executed.

In April, Iran's Supreme Court upheld the death sentence for German-Iranian Jamshid Sharmahd, 67, over his connection with a deadly mosque bombing in 2008.

At least 16 Western passport holders, most of them dual nationals, are currently detained in Iran.

Tehran insists all have gone through a proper judicial process.