The boss of Barclays refuses to resign over the rigging of the key lending rate between banks.
Bob Diamond has agreed to give evidence to MPs over the scandal which saw the bank fined £290m ($450m) on Wednesday by the UK and US authorities after an investigation into claims that several banks manipulated the Libor rate at which they lend to each other.
In the open letter he condemned the inappropriate behaviour of a "small number" of employees who tried to make profits for their own benefit.
He said: "When the trader conduct was first discovered by more senior management, steps were immediately taken to stop it, and it was reported to the authorities."
He added that Barclays was now "completing a review of employee conduct for all those involved", and that "all appropriate options will be pursued for those who have a case to answer, ranging from the clawback or withholding of remuneration to being asked to leave the bank".
On Thursday Prime Minister David Cameron said: "The whole management team [at Barclays] have got some serious questions to answer. Let them answer those questions first.
"Who was responsible? Who was going to take responsibility? How are they being held accountable?"
MPs including Tories Steve Baker and Nick De Bois are also pushing for Mr Diamond's resignation.
Barclays and the other banks involved now face the threat of criminal investigation in the UK over the scandal.
Barclays shares ended Thursday trading down 15.5%, RBS lost 11.5%, Lloyds went down 3.9%, and HSBC shares declined by 2.6%.