Clearstream, an international central securities depository based in Luxembourg, is being taken to court by the Central Bank of Iran, Bank Markazi.
Bank Markazi is seeking around $4.9 billion (€4 billion) in assets plus interest, Deutsche Börse, which owns 100% of Clearstream, said in a statement. Rome-based Banca UBAE is named as a co-defendent, it said.
The complaint was filed before a Luxembourg court.
"Clearstream believes the complaint against it to be without merit," Deutsche Börse said. "Clearstream will take all necessary and appropriate measures to vigorously contest the claims."
The new suit forms part of a long-running legal dispute in the US about Iranian assets, which were frozen on suspicion of terrorist financing and partly paid to victims of attacks.
The assests sought by Bank Markazi include $1.9 billion that was turned over to US plaintiffs after a court order in that country in 2013 in a proceeding that Bank Markazi was a party, Deutsche Börse said.
A further $2 billion of assets are currently subject to US and Luxembourg litigation brought by US plaintiffs.