Standard Chartered PLC is engaging in "constructive, ongoing discussions" with U.S. authorities regarding its past violations of Iran sanctions and is seeking an "acceptable resolution," The Wall Street Journal reported, citing a memo to senior staff, the contents of which a spokeswoman confirmed.

CEO Bill Winters said in the memo that most of the transactions in question were carried out before 2012, with none occurring after 2014, according to the Oct. 9 report.

In 2012, the bank agreed to pay fines totaling $667 million to settle alleged sanctions breaches between 2001 and 2007.

Bloomberg News earlier reported that StanChart could face a $1.5 billion penalty for Iran-related sanctions violations from regulators including the U.S. Justice Department, the Manhattan District Attorney and the New York State Department of Financial Services. Sources told the Journal that some of the regulators could lower their figures following negotiations with StanChart and to give credit for penalties by the other authorities.

The current investigation seeks to determine whether failures in StanChart's conduct and internal controls had enabled Iranian clients to continue doing business after 2007, when the bank formally halted its dealings with known Iranian parties, and whether the lender had fully informed regulators of any such lapses prior to its 2012 settlement, the Journal noted.

U.S. authorities are also looking at whether the bank violated compliance rules related to Iran as recently as 2013, Reuters reported, citing the memo.

The Financial Times recently reported that U.S. prosecutors are preparing to bring criminal charges against two former employees of the bank for allegedly breaches of Iranian sanctions.