"The three leading members have now been arrested and charged with espionage in Denmark on behalf of a Saudi intelligence service", PET said in a statement.
The search of their homes uncovered that the trio had collected information about people of interest in Denmark and abroad and passed it on to Saudis from 2012 to 2018.
"Obviously, this is a very serious case. We cannot and will not accept that foreign states bring their mutual conflicts to this country", PET chief Finn Borch Andersen was quoted as saying.
The three were initially probed to determine whether their public approval of a terror attack on a military parade in Iran in 2018 amounted to support of terrorism. Their organization is outlawed in Iran.
ASMLA is vying for a separate Arab state in Iran’s oil-rich southwestern province of Khuzestan. Iran has accused Saudi Arabia of helping groups that seek to overthrow the government.
Separately, the Danish intelligence agency charged a fourth Iranian in absentia on Monday with spying and plotting a murder attempt that was thwarted in Denmark in 2018, the public DR broadcaster reported.