LONDON - Standard Chartered Chief Executive Bill Winters hit back at critical media coverage of the bank's attempts to improve its financial crime controls, in a memo sent to hundreds of senior managers at the bank on Tuesday.

Winters sought to reassure staff about StanChart's recent financial performance and progress mending flaws in regulatory compliance, after media reported last week that the lender faced a possible $1.5 billion fine for past Iran-related sanctions violations.

"You'll have undoubtedly seen recent articles commenting on our financial performance and speculating about a financial penalty for the U.S. investigation regarding our historical sanctions conduct and controls," Winters wrote in the memo obtained by Reuters.

"I'd like to briefly address each because I don't think they reflect the progress we are making as a Bank," Winters wrote.

A spokesman for the London-based bank confirmed the contents of the memo but declined to comment further.

The unusual step of criticising media coverage in a memo sent to hundreds of the bank's 'business leadership team' reflects a bolder stance in StanChart's efforts to rehabilitate its public image following years of costly fines.

Media reports last week said the fine of around $1.5 billion was a preliminary assessment based on some of the communications between the bank and regulators, and that final discussions had not yet begun.

StanChart last week declined to comment on the size of the possible fine but said it was "engaged in ongoing discussions with U.S. authorities".

The bank has been subject to a deferred prosecution agreement (DPA) with the United States since 2012. The DPA was extended in 2014 and again earlier this year. It is due to expire in December.

The current negotiations with U.S. authorities and the possible fine relate to whether the bank violated Iranian sanctions after 2007, when it said it would no longer do business with Iran-related entities.

(Reporting by Lawrence White Editing by Sinead Cruise/Edmund Blair/Susan Fenton) ((lawrence.white@thomsonreuters.com; +44 207 542 6137; Reuters Messaging: lawrence.white.thomsonreuters@reuters.net))