Austria is preparing to strip the diplomatic immunity from an Iranian envoy suspected of planning to bomb Iranian politicians in France.
The diplomat and two other arrested people are suspected of plotting to attack a meeting of exiled opposition members in Paris last weekend.
Tehran denies any involvement.
The diplomatic tension comes a day before President Hassan Rouhani is due to arrive in Austria to discuss a disputed nuclear deal.
Two Belgian nationals apprehended in Brussels are reported to be husband and wife, and to be of Iranian origin.
The Iranian diplomat, identified as Assadollah A, is ordinarily based in the Austrian capital. But he was arrested in Germany.
Iranian foreign ministry spokesman Bahram Qassemi told reporters that his country had evidence that the attack had been planned by a terrorist organisation.
“The latest scenario has been planned and carried out to damage Iran-Europe ties amid such sensitive and crucial times,” he said.
What was the alleged bomb plot?
The group portrays itself as a parliament-in-exile, made up of a wide array of disparate groups. It says “tens of thousands” attended the weekend’s rally at the Paris Convention Centre.
On Saturday, the day of the rally, the two Belgian nationals were caught by Belgian police, with half a kilogram (1.1lb) of homemade explosives along with a…