The new investigation is a potential blow to the banks as they have already paid billions of dollars in penalties and fines to various federal agencies following scrutiny of their conduct leading up to and during the market panic of 2008.

Banks continued to hold billions of dollars in hard-to-price assets on their books even in the aftermath of the credit crisis.

Regulators are now seeking information about whether banks made "significant misrepresentations" about some of those assets to make deals, the Journal said. (http://link.reuters.com/xad85v)

The probe focuses on whether traders bought or sold residential mortgage-backed securities at artificially depressed or inflated values from around 2009 through 2011, the paper said.

The other parties in such deals would typically be rival banks, hedge funds and other large investment firms, according to the paper.

The banks being probed include Barclays Plc (>> Barclays PLC), Citigroup Inc (>> Citigroup Inc), Deutsche Bank (>> Deutsche Bank AG), Goldman Sachs Group Inc (>> Goldman Sachs Group Inc), JPMorgan Chase (>> JPMorgan Chase & Co.), Morgan Stanley (>> Morgan Stanley), Royal Bank of Scotland Group (>> Royal Bank of Scotland Group plc) and UBS AG (>> UBS AG).

The investigation, which began less than a year ago, is still at an early stage and may not lead to enforcement action. Subpoenas have been sent to several firms to gather information, according to the newspaper.

The probe is being conducted by the Securities and Exchange (SEC) and the special inspector general for the Troubled Asset Relief Program (Sigtarp).

Spokesmen for the SEC, Sigtarp and JPMorgan declined to comment to the newspaper.

RBS spokeswoman Mary Taylor declined to comment to Reuters on the Journal report.

None of the other parties could immediately be reached for comment by Reuters outside of regular U.S. business hours.

(Reporting by Sakthi Prasad and Sruthi Ramakrishnan in Bangalore; Editing by Supriya Kurane)