Authorities in Iran say they have detained the leader of a U.S.-based opposition group it accuses of involvement in a 2008 bombing and of plotting other attacks.

The Intelligence Ministry said on August 1 that it had detained Jamshid Sharmahd of the little-known Kingdom Assembly of Iran, or Tondar.

It said in a statement that security forces arrested Sharmahd in a “complicated operation,” but did not specify how, where, or when the detention took place.

Iranian television showed a video of a man identifying himself as Sharmahd giving a confession. Iran is known to use torture to force confessions from prisoners.

A U.S. State Department spokeswoman told Reuters that the U.S. government was "aware of reports” of Sharmahd’s detention.

“The Iranian regime has a long history of detaining Iranians and foreign nationals on spurious charges. We urge Iran to be fully transparent and abide by all international legal standards,” the spokeswoman said.

Tondar did not immediately respond to e-mails from RFE/RL. Two telephone numbers on its website no longer work.

In a statement on its website, the group mentioned an “abduction” of Sharmahd without explicitly confirming "stories of various networks.”

Based in Los Angeles, Tondar says it aims to overthrow the Islamic republic and reestablish a monarchy similar to that of Cyrus the Great. It runs pro-Iranian opposition radio and television stations abroad, as well as social media channels.

According to the group's website, Sharmahd is an Iranian-German electronics engineer born in Tehran in 1955 who had lived in Germany before moving to Los Angeles in 2003.

The Intelligence Ministry said the group “directed armed and terrorist acts in Iran from America.”

It alleged that Sharmahd planned and directed an explosion at a religious center in the southern city of Shiraz in 2008 that killed 14 people and wounded 215.

It also claimed Iranian intelligence had foiled several other attacks over the years, including on a dam in Shiraz, at the Imam Khomeini Mausoleum, and the Tehran Book Fair.

According to some media reports, Sharmahd claimed responsibility for the Shiraz blast. Tondar’s website says Iranian authorities blamed the group for the Shiraz attack after it had broadcast information about it. In 2009, Iran executed three men convicted of involvement in the 2008 bombing.

Tondar says the three men were members of the group.

Tondar has claimed responsibility for some attacks, including the bombing of a seminary used by the Islamic Revolutionary Guards Corps (IRGC) in Shiraz in June 2019.

It also claimed credit for an explosion at a refinery in 2016.

In 2007, Tondar’s founder, Frood Fouladvand, and two other members of the group disappeared in what Amnesty International described as a likely Iranian intelligence operation in Hakkari Province on the border with Turkey.

Intelligence Minister Mahmoud Alavi called Tondar the "most violence-prone" royalist opposition group.

"Despite our complaint to Interpol, Sharmahd would travel everywhere under his own name. This shows how empty anti-terror slogans by Americans and their Europeans allies are," he told state TV.

The detention under unknown circumstances comes as tensions between the United States and Iran have escalated since the United States withdrew from the international Iran nuclear deal in 2018 and reimposed crushing sanctions.

The United States has also accused Iran of destabilizing the Middle East and supporting militias and terrorist groups across the region.

While overshadowed by other exiled opposition groups, Iran reportedly brought up Tondar multiple times while negotiating the terms of the 2015 deal.

Iranian Foreign Minister Mohammad Javad Zarif accused the West of “hypocrisy.”

“The west must cease financing and harboring terrorists,” he said on Twitter.

Iran is known to have assassinated and abducted multiple exiled opposition figures in the past.

With reporting by Radio Farda, AFP, AP, and Reuters