Iran arrested several members of the Baha’i faith on spying charges, authorities said Monday, the latest sign of a tightening crackdown across the Islamic Republic as it faces international pressure over its tattered nuclear deal.

The Baha’i demanded their release and called their arrests part of a long pattern of persecution by Iran’s Shiite theocracy.

Iran’s Intelligence Ministry said in a statement that the suspects were linked to the Baha’i center in Israel and had collected and transferred information there.

The Baha’i’s international governing body, the Universal House of Justice, long has been based in Haifa, Israel. The Baha’i have had a presence there since before the founding of the state of Israel, which the Islamic Republic views as its chief enemy in the region.

Iran offered no evidence to support the allegations of the Baha’i doing anything illegal. State TV footage showed one of the suspects saying he was being monitored by agents of the ministry, though he did not acknowledge in the footage doing anything wrong.

The Baha’i through an international advocacy group identified several of those arrested as leaders in their religion who previously served 10-year prison sentences.

They are “domestic symbols of resilience and internationally renowned former prisoners of conscience,” the Baha’i said. “Arresting them reveals the Iranian government’s escalating persecution of Iran’s Baha’i community.”

Iran already bans the Baha’i, a religion founded in the 1860s by a Persian nobleman considered a prophet by his followers. Muslims consider the Prophet Muhammad the highest prophet.

The Baha’i say they’ve been persecuted by Shiite clerics in Iran since their religion’s founding — something that’s grown more intense since the 1979 Islamic Revolution.

In 2013, Iran’s Supreme Leader Ali Khamenei, who has final say on all state matters, urged Iranians to avoid all dealings with the Baha’i. Khamenei’s fatwa, or religious order, supported similar fatwas in the past by other clerics.

The detention of the Baha’i follow a wave of recent arrests as tensions escalate between Iran’s hard-line government and the West. Security forces have detained film directors, several foreigners and a prominent reformist politician as talks to revive Tehran’s nuclear accord with world powers hit a deadlock and fears grow over the country’s economic crisis.

AP