COPENHAGEN (Reuters) - Denmark said on Monday it had arrested three leading members of an Iranian Arab opposition group on suspicion of spying for Saudi Arabia.

The three members of the Arab Struggle Movement for the Liberation of Ahvaz (ASMLA) had already been charged by Danish police for supporting an attack in Iran in 2018.

“It is the view of PET (The Danish Security and Intelligence Service) that the three people, in the period from 2012 to 2018, have been spying for a Saudi Arabian intelligence service,” PET chief Finn Borch Andersen told reporters.

The three Iranians have been under close police protection and one was the subject of a 2018 assassination plot that was prevented by PET after a major police operation.

In 2017, Ahmad Mola Nissi, an Iranian exile who established ASMLA, was shot dead in the Netherlands.

PET said a Norwegian citizen of Iranian background, who was held in connection with the plot in October 2018, was still under arrest.

In addition, it said it had on Monday arrested in absentia a member of the Iranian intelligence service on suspicion of espionage and complicity in the 2018 murder attempt.

The Iranian government has previously denied any connection with the alleged plot.

ASMLA seeks a separate state for ethnic Arabs in Iran’s oil-producing southwestern province of Khuzestan. Arabs are a minority in Iran, and some see themselves as under Persian occupation and want independence or autonomy.