Iranian assets of nearly one billion pounds’ ($1.64 billion) are frozen in Britain under international sanctions imposed over Tehran’s nuclear program, the British government said on Thursday.

“The total assets frozen in the UK under the EU (European Union) and U.N. sanctions against Iran are approximately 976,110,000 pounds,” Ian Pearson, economic secretary to the Treasury, said in a written statement to parliament.

The statement gave no further details.

Iran has been gripped this week by its most violent demonstrations since the 1979 Islamic revolution, sparked by its disputed presidential election last Friday.

The U.N. Security Council has imposed three sets of sanctions on Iran since 2006 over its nuclear program, which Western powers suspect is aimed at developing atomic weapons. Tehran says its program is designed only to generate electricity.

The U.N. sanctions include freezing assets of, companies and people alleged to be engaged in or supporting sensitive nuclear work or the development of ballistic missiles, including state-run Bank Sepah and firms controlled by the Revolutionary Guards.

The EU has frozen assets of Iran‘s biggest bank, Bank Melli.