By Jessica Hodgson

LONDON--U.S. and U.K. authorities are talking to Royal Bank of Scotland Group PLC (RBS) about the possibility that it breached sanctions on Iran, a person familiar with the matter said Wednesday, days after the U.K.'s Standard Chartered PLC (STAN.LN) settled with a New York regulator amid allegations that it broke U.S. money-laundering rules on Iran.

The person said that RBS, which is 82%-owned by the U.K. taxpayer, was in negotiations with the U.S. Federal Reserve and Department of Justice on whether it had complied with economic sanctions on Iran. The person stressed that the discussions had been initiated by RBS' current management, as opposed to the authorities. Two people familiar with the matter said the U.K.'s Financial Services Authority was also talking to RBS.

An RBS spokeswoman pointed to disclosures made alongside the bank's half-year results earlier this month--which she said had first been disclosed 18 months ago--that the bank "has initiated discussions with U.K. and U.S. authorities to discuss its historical compliance with applicable laws and regulations, including U.S. sanctions regulations."

RBS "may become subject to formal and informal supervisory actions and may be required by its U.S. banking supervisors to take further actions and implement additional remedial measures," the half-year statement continued, warning that these actions "could have a material adverse effect on the group's net assets, operating results or cash flows in any particular period."

The statement didn't name Iran, but the person familiar with the matter confirmed that many of the questions on historical compliance relate to whether RBS complied with Iran sanctions.

RBS' disclosure raises the possibility that it may ultimately face a fine, adding to a long list of issues the Edinburgh-based bank is grappling with as it seeks to pare back a previously bloated balance sheet and restore a reputation that was damaged by its near-collapse in the aftermath of the financial crisis. The bank was bailed out by the U.K. government in 2008.

The bank has pledged to get rid of the bulk of the remnants from a troubled history of acquisitions and ill-fated expansions by the end of 2013. Earlier this month, RBS said that noncore assets had shrunk to GBP72 billion ($112.3 billion) from the peak of GBP258 billion reached in 2008, just after RBS had to be saved by U.K. taxpayers.

It also comes against a backdrop of a wave of scandal that has hit British banks this summer, setting back their attempts to recover from the financial crisis.

Barclays PLC (BCS) in June said it had settled with U.K. and U.S. regulators to the tune of GBP290 million amid accusations its traders had deliberately rigged a benchmark interest rate, the so-called London Interbank Offered Rate.

That scandal, which led ultimately to the departure of bank Chairman Marcus Agius, Chief Executive Bob Diamond and Chief Operating Officer Jerry del Missier, followed a political uproar that saw senior executives hauled in front of a committee of lawmakers. A number of other major world banks--among them RBS--remain under investigation by authorities over alleged Libor manipulation.

Shortly after the Barclays scandal, a U.S. Senate committee attacked HSBC Holdings PLC (HBC) for allegedly handling money for drug gangs and terrorist groups. In a statement accompanying the U.S. Senate hearing, HSBC said it recognized "that its controls could and should have been stronger and more effective in order to spot and deal with unacceptable behavior."

Standard Chartered weeks ago agreed to pay $340 million to a New York regulator to settle allegations that the bank broke U.S. money-laundering laws in handling transactions for Iranian customers, after a weeklong, transatlantic regulatory drama.

The person said that the New York regulator that made the accusations against Standard Chartered, the Department of Financial Services, isn't talking to RBS.

-Write to jessica.hodgson@dowjones.com

(Max Colchester contributed to this article.)