Iran reacted furiously on Thursday to a United States Supreme Court ruling that Iran’s central bank must pay nearly $2 billion to American victims of terrorist attacks, calling the ruling thievery and a new threat to any improvement in relations.

A spokesman for the Iranian Foreign Ministry, Hossein Jaberi Ansari, said in a statement quoted by state media that the court’s ruling on Wednesday was a mockery of international law and “amounts to appropriation of the Islamic Republic of Iran’s property.”

Congress enacted a law in 2012 to make it easier for families of Americans killed in terrorist attacks, like the 1983 truck bombing of a Marine Corps barracks in Beirut, Lebanon, to recover damages from Iran. Investigators have concluded that Iran was responsible for that attack, something Iran has long denied.

The court ruled 6 to 2 that Congress did not exceed its constitutional role in enacting the law. The ruling will, at least theoretically, allow the families to obtain compensation from Iranian central bank assets that have been impounded.