HSBC plans to "acknowledge and apologize" for failing to spot and deal with money laundering within the bank during a U.S. Senate panel hearing next week, according to an internal memo sent by its chief executive.

"It is right that we are held accountable and that we take responsibility for fixing what went wrong," Chief Executive Officer Stuart Gulliver said in a note sent to staff and seen by Reuters.

The U.S. Senate Permanent Subcommittee on Investigations has been investigating HSBC for months as part of an effort by Congress to probe shadowy money flows. The title of the hearing is "Vulnerabilities to Money Laundering, Drugs, and Terrorist Financing: HSBC Case History."

The Senate committee will release a list of people they plan to call up later this week.

HSBC spokesman Gareth Hewett declined to comment on the memo, but said the bank plans to "fully cooperate" with any investigations.

The appearance by Europe's biggest bank at the committee hearing comes about a week after Barclays former chief executive Bob Diamond appeared before a parliamentary inquiry in Britain for its role in fixing the rate at which banks lend to each other.

Reuters originally reported in January that HSBC was under Senate investigation. Reuters subsequently reported in May that the bank has been the subject of an investigation by two U.S. Attorney offices.

HSBC also is under investigation by the U.S. Securities and Exchange Commission and the Justice Department. Those probes also are examining whether HSBC was vulnerable to illicit funds moving through the bank.