In an alleged plot that has taken weeks to come to light, Denmark has accused Iran of planning to assassinate an activist on its soil.
Iran has dismissed the allegations. But Denmark has recalled its ambassador from Tehran and is speaking to other EU countries about how to respond.
Both countries had already clashed this year after a deadly shooting at an Iranian military parade in September.
Iran accused Denmark, the Netherlands and Britain of harbouring members of militant opposition groups following the deadly attack, in which more than 25 people were killed.
One of those groups is at the centre of Denmark’s murder plot allegation.
Their claim also comes as the EU tries to save a landmark nuclear deal with Iran, from which the US has already withdrawn.
In August, the Trump administration reimposed sanctions on the country, and a second wave comes into force on 5 November.
So what does Denmark say happened? What’s been the response? And has this happened elsewhere in Europe?
What happened in the investigation?
The drama started in September, when – seemingly from nowhere – a large area around Denmark’s capital Copenhagen was cut off.
Police closed bridges, boats and trains to and from Zealand, Denmark’s largest island, in a massive hunt for a Swedish-registered black Volvo.
Three people involved in a “serious crime” were in the car, an official statement said at the time. “Witnesses who see the vehicle should contact the police immediately,” it added.
After hours of confusion and travel chaos, the authorities reopened all transport links and apologised, saying in a tweet there was nothing new to report on the case.
Rumours have circulated ever since about what prompted the unprecedented action, which came just six days after the Iranian military parade was attacked.
On Tuesday, the shocking answer came.
Finn Borch Andersen, head of Denmark’s intelligence service Politiets Efterretningstjeneste (PET), said the agency believed Iran “was planning an attack in Denmark” against three activists.
The trio, who live in the city of Ringsted, south-west of Copenhagen, are part of the separatist Arab Struggle Movement for the Liberation of al-Ahwaz (ASMLA).
What is ASMLA?
The Arab Struggle Movement for the Liberation of al-Ahwaz was set up in 1999, and is classified as a terrorist group in Iran
ASMLA is one of several groups that wants a separate Arab state in the country’s south-western Khuzestan Province
It split in two in 2015, with one faction based in the Netherlands and the other based in Denmark. Both groups are called ASMLA
Group founder Ahmad Mola Nissi was shot dead in November 2017 outside his home in the Netherlands
PET says days before the manhunt on 28 September, agents saw an individual taking photos of the ASMLA branch leader’s home.
At Tuesday’s press conference, the PET chief said they thought this person – a Norwegian citizen of Iranian origin – planned to give the pictures to Iran, which could be used to plan an attack on Danish soil.
Agents were further concerned when a Swedish-registered black Volvo starting moving “suspiciously” outside the house, Mr Andersen said.
When they tried to stop the car, it sped off – prompting fears of an imminent attack.
This was the reason behind the road closures and the epic manhunt for the vehicle.
Danish newspaper Politiken reports that the authorities have since spoken to the Volvo passengers, and decided the car had nothing to do with the case.
But in October, the man who took photos of the ASMLA leader’s home was arrested in the Swedish city of Gothenburg.
Swedish security forces say he has now been extradited to Denmark.
“We are dealing with an Iranian intelligence agency planning an attack on Danish soil,” PET chief Andersen told the press conference. “Obviously, we can’t and won’t accept that.”
Although no details have emerged about how PET found out about the man, Israeli public broadcaster KAN reports that information from spy agency Mossad helped lead to the arrest. Israeli government officials declined to comment.
What’s been the response?
Iran was quick to dismiss the claims as fiction.
Foreign ministry spokesman Bahram Qasemi said such “biased reports” and allegations pursued “the enemy’s plots and conspiracies” to harm the developing relations between his country and Europe, according to Tasnim news agency.
But Danish Prime Minister Lars Lokke Rasmussen called the alleged assassination plot “totally unacceptable”.
He said UK Prime Minister Theresa May had voiced support for Denmark in a meeting in Oslo.
Denmark’s Foreign Minister, Anders Samuelsen, said the country was discussing possible action with other European countries.
Are the claims true?
Former PET chief Hans Jorgen Bonnichsen told Danish broadcaster DR it was “very rare” to have one intelligence agency making claims against another, as it could cause a rupture in international relations.
“PET has really thought about it before choosing that step,” he said.
Only six days before Denmark shut down all its transport links to Zealand, an Iranian military parade was attacked in its south-western city of Ahvaz.
A spokesman for Denmark-based ASLMA said the al-Ahwaz National Resistance, an umbrella movement for Arab separatist groups fighting for independence for Khuzestan province, carried out the attack. But several of the other separatist groups denied any involvement.
The Islamic State group also claimed the shooting and published a video purportedly showing three of the gunmen being driven to the military parade in a car.
The men appeared to be dressed in Revolutionary Guards uniforms and talk about the importance of jihad. However, none of them stated that they were members of IS or pledged allegiance to the group’s leader, Abu-Bakr al-Baghdadi – something that is common in such pre-attack videos.
Iranian officials said they believed the gunmen had links to an “Ahvazi terrorist group”.
In October, France accused Iran of an alleged bomb plot to attack exiled Iranian opposition members in Paris.
In June, allegations emerged that Iran was behind the assassination of a mannamed by police as Ali Motamed near Amsterdam in 2015.
The 56-year-old is suspected of being Mohammad Reza Kolahi Samadi, who was accused of planting a bomb which resulted in the deadliest attack in modern Iranian history. Iran denies any involvement.
And in May, the US Secretary of State made a speech asserting Iran’s elite Quds Force “conducts covert assassination operations in the heart of Europe”.
Mr Pompeo did not substantiate the claims at the time, and they were met with confusion in Europe.
There have been no recent killings in Europe officially attributed to Iran.