But the plot was stopped when a Norwegian citizen of Iranian background - said to be linked to the assassination attempt - was arrested in Sweden on October 21 and extradited to neighbouring Denmark.
British premier Theresa May quickly voiced support for Denmark's position during a meeting in Oslo of northern European leaders, and Danish leader Lars Lokke Rasmussen tweeted his appreciation, adding his determination to "stand up to Iran" together with the U.K, and other countries.
"Obviously, we can't and won't accept that".
Denmark has recalled its ambassador to Tehran, summoned on Wednesday, before his departure, the ministry of foreign Affairs in the iranian capital.
Borch Andersen emphasized that the arrest of the Norwegian citizen "does not mean that the threat [against the Iranian target in Denmark] has been minimized".
"We want to preserve the nuclear agreement", Lokke Rasmussen said, referring to how possible sanctions would approach the 2015 global accord on Iran's nuclear programme.
The Ahwazi are fighting for a separate state in Arabic-speaking Ahvaz province, with a number of militants attacks launched in Iran - mostly against infrastructure.
US President Donald Trump pulled the US out of the Iran accord - known officially as the Joint Comprehensive Plan of Action (JCPOA) - in May, slamming it as a bad deal and reimposing punishing sanctions on Iran.
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The Israeli intelligence agency provided key information to its Danish counterpart to save Iranian dissidents from being murdered by Iranian government agents.
Denmark said on Wednesday it was consulting with its allies about possible sanctions against Iran after accusing Tehran of plotting an attack against Iranian dissidents living in the Scandinavian country.
On Tuesday, Iranian Foreign Ministry spokesman Bahram Qasemi dismissed the claim and said it was in line "with the enemies' plots and conspiracies against the good and ever-growing Iran-Europe relations under present grave and special conditions", according to state-run IRNA news.
Samuelsen said Iran's ambassador to Denmark, Morteza Moradian, had been summoned to the Foreign Ministry in Copenhagen and it was made "crystal clear" to him that "the gravity of the matter is hard to describe".
Several Danish media reports have discussed the possible wider worldwide ramifications, as well as the pattern of suspected Iranian government operations in other European countries.
In September, Tehran accused Denmark, the Netherlands and Britain of harbouring opposition members that Iran accuses of being responsible for the military parade attack in Ahvaz.
The so-called Islamic State group and a separatist Arab group claimed responsibility, and Iran staged several operations in Iraq and Syria in response.