Updated

A massive police operation in eastern Denmark last month was part of attempts to thwart an Iranian intelligence plot to kill an opposition activist, the country's intelligence agency boss said Tuesday.

Finn Borch Andersen said police on Sept. 28 were searching for a stolen, Swedish-registered car when they briefly cut off the island where Copenhagen sits from the rest of the country and closed the borders with Germany and Sweden. They later found it had no connection with the case.

A Norwegian citizen of Iranian descent was arrested Oct. 21 on suspicion of helping an unknown Iranian intelligence service "to act in Denmark" and for involvement in planning to kill an opposition member, Borch Andersen said.

The suspect, who was not identified, is in pre-trial custody until Nov. 8. He denies any wrongdoing, said Borch Andersen, adding that intelligence agencies in Sweden and Norway cooperated in the connection with the arrest. He did not give details.

The person had, among others, been seen taking photos of the residences of members of the Arab Struggle Movement for the Liberation of Ahwaz (ASMLA) in Ringsted, nearly 60 kilometers (37 miles) southwest of Copenhagen.

The group has been named by Tehran as being behind a terror attack on a military parade in the city of Ahvaz on Sept. 22 that left at least 25 people dead. It has condemned the attack and said it was not involved.

After that attack, Tehran summoned Denmark's ambassador and accused the Danish government of harboring members of the "terrorist group."

On Twitter Tuesday, Foreign Minister Anders Samuelsen called it "totally unacceptable" that Iran was planning an attack in Denmark. The country will react toward Iran and will speak with its European partners about "further steps," he said, without giving details.

Borch Andersen said Denmark has worked and is working "with a series of partners in Europe on the case but stopped short of saying who they were.

During the televised press conference, the head of the intelligence service also noted that Iran earlier had been active against opposition groups abroad. He singled out a foiled bombing attack that targeted a rally organized by an Iranian opposition group near Paris in June.