FRANKFURT (Reuters) - Deutsche Bank has widened an internal probe into possible manipulation of the Libor benchmark interest rate after discovering a new chatroom where traders may have colluded, a source familiar with the matter said on Monday.
Another source said Deutsche had summoned around 50 employees for questioning as a result of the discovery. The bank declined to comment.
More than a dozen banks and brokerage firms, including JP Morgan and Citigroup, are being investigated by regulators over the possible manipulation of benchmark interest rates -- including the London interbank offered rate, known as Libor -- which are used to price trillions of dollars' worth of loans.
Deutsche says it is cooperating with investigators, but has also conducted an internal inquiry, led by its legal department, which resulted in the suspension of five Frankfurt-based traders in February.
Four of these traders successfully sued Deutsche for unfair dismissal in September, and revealed fresh evidence about how the bank set interbank lending rates.
Last week it emerged that the German markets regulator BaFin now wants to speak to another former Deutsche Bank trader, Christian Bittar, as part of its Libor probe.
BaFin had already investigated Deutsche for over a year and handed over a report of its findings in August, having found no wrongdoing at the bank's management. But it said at the time that it would continue the probe if new facts came to light.
BaFin's investigation has focused on organisational issues, examining in particular whether banks reacted quickly enough once the Libor problems became known, and whether they reached the right conclusions.
Deutsche Bank changed its rules about Libor submissions in March 2012, and its rules on setting Euribor, the euro interbank offered rate, in July 2012. It has already made provisions for possible fines in the case, sources close to the bank have told Reuters.
For their roles in the Libor scandal, Switzerland's UBS agreed to pay penalties of $1.5 billion and Britain's Barclays has paid $453 million.
(Reporting by Philipp Halstrick, Kathrin Jones, Edward Taylor and Alexander Huebner; Editing by Noah Barkin and Kevin Liffey)