Federal prosecutors have begun a probe into the Wells Fargo bogus accounts scandal, the Wall Street Journal reported.

The investigation, which is at an early stage, is looking at whether senior bankers directed lower-ranking employees to falsify documents in conjunction with two million accounts that were opened without customer knowledge, said the newspaper.

The probe, which is led by the US attorneys from New York and California, is also looking at whether senior executives willfully turned a blind eye to the practices, said the Journal, which cited unnamed sources.

Wells Fargo has fired 5,300 employees connected to the problem. Chief executive John Stumpf told the newspaper the scandal did not signify wider cultural problems within the bank.

Prosectors have issued a subpoena for documents connected to the matter, according to the report.

Wells Fargo has been under fire since regulators fined the big US bank $185 million for opening more than two million deposit and credit card accounts without customer authorization.

Treasury Secretary Jacob Lew said Tuesday's that Wells Fargo's scandal constituted "unacceptable behavior" that must be punished.

Wells Fargo declined comment.