Authorities in the U.S. and UK are on the verge of filing criminal charges against former employees of Barclays Plc (NYSE: BCS), for their alleged role in rigging the London Interbank Offered Rate, or Libor, the Wall Street Journal reported.

Citing people familiar with the plans, the Journal said that criminal charges are likely to be filed as early as this summer, but it is not yet clear which former employees from Barclays are being targeted or what the charges would be. The sources also added that plans are not final and “could be delayed or modified,” according to the report.

The investigation, which began since the scandal came to light in 2008, has brought several global financial institutions under the regulators' scanner for their alleged roles in manipulating the Libor and other global benchmark interest rates.

The reports of possible arrests of traders had emerged in the media last year, but so far, the investigations on the scandal had been limited to the banks and other financial institutions, and not their employees.

The newspaper, quoting people familiar with the investigations, reported that authorities from the Serious Fraud Office and the Financial Conduct Authority, both in London, are probing several criminal and civil charges against former Barclays employees.     

The sources also told the newspaper that the Barclays employees targeted in the present investigation are mid-level traders and not top-rung executives.

However, some question the move to target traders when top executives who might have been involved in the decision-making process in connection with the alleged Libor manipulations are left out of the investigations. Although U.S. and British investigators initially said they would bring charges against every institution and individual involved in the scandal, the investigation has not made much progress in this direction, critics claim.

The U.S. Justice Department is also developing criminal cases against some former Barclays employees, according to media reports.

Barclays, in June 2012, admitted that it was acting to artificially lower the Libor throughout 2007 and 2008. The bank entered an agreement with the Department of Justice to pay a $160 million penalty to resolve violations arising from the bank's manipulations of the Libor and other benchmark interest rates used in financial markets.

Barclays, since the allegations surfaced, has fired several employees, including top executives, allegedly involved in the Libor scandal.

Units of two other banks, UBS AG (NYSE:UBS) and Royal Bank of Scotland Group PLC (NYSE:RBS) have also pleaded guilty to criminal charges in the U.S. stemming from alleged manipulation of interest rates. So far, U.S. authorities have filed charges against two former UBS employees in connection with the Libor allegations.

According to earlier reports, regulators are also said to be investigating Michael Zrihen at Credit Agricole, Didier Sander at HSBC -- who according to the Telegraph exchanged emails with Barclays' Philippe Moryoussef -- and Christian Bittar at Deutsche Bank. However, HSBC (NYSE:HBC) is not connected with the Libor scandal investigations, the bank said.