U.S. officials are investigating possible violations of sanctions against Iran by Royal Bank of Scotland, Britain's Financial Times reported Wednesday..

The part-nationalized bank declined to comment except to repeat previous disclosures that it is in contact with U.S. and British authorities "to discuss its historical compliance with applicable laws and regulations, including U.S. economic sanctions regulations."

The Financial Times says the U.S. Department of Justice and the Federal Reserve investigations were prompted by voluntary disclosures made by the bank about 18 months ago.

Two years ago, Royal Bank of Scotland was fined $500 million by U.S. regulators for money-laundering activities by the Dutch bank ABN Amro, which was taken over in 2007 by a consortium led by RBS.

ABN Amro was found to have conspired to handle illegal U.S. dollar transactions for customers from Iran, Libya, the Sudan, Cuba and other countries subject to U.S. sanctions.

Another British bank, Standard Chartered, agreed this month to pay $340 million to a New York regulator to settle accusations that it hid illegal transactions with Iran and violated U.S. sanctions law. Investigations by other U.S. agencies are continuing in that case.

RBS, which is 82 percent owned by British taxpayers, consented last year to a cease and desist order which required it to remedy deficiencies in governance, risk management and compliance controls which had been identified in 2010 by the U.S. Federal Reserve and statement banking supervisors.

In its half-year results published earlier this month, RBS said various units of the group had been named as defendants in suits filed in the U.S. related to claims that it was involved in manipulating the London interbank offered rate (LIBOR), a widely used market index.

"The group considers that it has substantial and credible legal and factual defenses to these and prospective claims," RBS said.

RBS also said it was cooperating with LIBOR investigations by U.S. agencies and by the Japanese Financial Services Agency, the European Commission and the Canadian Competition.

In June, Barclays PLC agreed to fines totaling more than $453 million in fines after admitting that bank employees had submitted false reports of interbank borrowing rates used to calculate LIBOR.