LONDON — The European Union penalized Iran on Tuesday over allegations that the country’s intelligence service orchestrated a series of assassination plots in Europe in recent years, including the killing of two Iranians in the Netherlands with ties to anti-government extremist groups.

In a letter outlining its justification for sanctions, the Dutch Foreign Ministry cited “strong indications that Iran was involved in the assassinations of two Dutch nationals of Iranian origin,” one in 2015 in the city of Almere and another in 2017 in The Hague.

European intelligence officials have also linked the Iranian government to unsuccessful plots in Denmark and France.

“In the Dutch government’s opinion, hostile acts of this kind flagrantly violate the sovereignty of the Netherlands and are unacceptable,” the letter said.