DBS Bank says it is tightening checks and controls after it was implicated in the 1MDB case, which is now being investigated by the Monetary Authority of Singapore (MAS).

DBS is one of the banks named by the authority as having had "failings" in controls and "weaknesses in the process for accepting clients and monitoring transactions" related to 1MDB.

"We already tightened up a lot compared to 2013, partly because the MAS has also been tightening the standards over the last two to three years," DBS Group chief executive Piyush Gupta said.

However, Gupta said, "a lot" of due diligence was done when the bank accepted the clients three years ago.

"In hindsight, were the accounts part of a complex (network)? Probably. Could we have done better in figuring it out? Of course we could have," he is quoted as saying by Singapore's Straits Times.

It is not clear if DBS, Singapore's top lender, will be fined as investigations are ongoing.

Other banks facing regulator scrutiny over 1MDB include Standard Chartered, UBS, Switzerland's Falcon Private Bank and Coutts International.

Singapore regulators have also shut down Swiss bank BSI for its dealings with 1MDB.