Denmark’s intelligence service accused Tehran of plotting an attack against three Iranians living in the Scandinavian country, in response to a deadly attack in Iran in late September.

“It was an operation by the Iranian intelligence service which, we believe, was planning an attack in Denmark” against three Iranians suspected of belonging to the Arab Struggle Movement for the Liberation of Ahvaz, Danish Security and Intelligence Service (Politiets Efterretningstjeneste, PET) chief Finn Borch Andersen told reporters on Tuesday, October 30.

A Norwegian of Iranian origin was arrested on October 21 and placed in custody, suspected of planning the attack and spying for Iran.

The suspect was detained in Sweden, according to the Swedish security service Sapo. He will be held in isolation until November 8 and has maintained his innocence, The Local reported.

The target of the attack and two other members of the group are under police protection, Andersen said.

At the end of September, Tehran had accused Denmark, the Netherlands and Britain of “hosting several members of the terrorist group” that Iran accuses of being responsible for an attack in the mainly ethnic Arab city of Ahvaz in southwestern Iran.

The September 22 attack, in which five commandos opened fire on a military parade, left 24 people dead. A separatist Arab group called Ahvaz National Resistance and Islamic State both claimed responsibility for the attack.

In retaliation, Iran fired ballistic missiles into eastern Syria at what the Islamic Revolutionary Guard Corps said was a terrorist headquarters.

Tehran’s operation in Denmark was “completely unacceptable,” Danish Foreign Minister Anders Samuelsen wrote on Twitter on Tuesday.

“The government will respond to Iran and speak to its European partners about further measures,” he added.

Iran’s ambassador to Copenhagen was summoned to the foreign ministry for an explanation on Tuesday.

PET’s announcement ends weeks of media speculation about why Denmark shut down bridges to Sweden and ferries for several hours on September 28 in a massive manhunt that mobilized hundreds of police and the military.

The shutdown was aimed at preventing the Iranian operation, PET acknowledged on Tuesday.

Police were searching that day for a stolen Sweden-registered car that was later found to have no connection with the case, the Associated Press reported Andersen as saying.

With reporting from AFP