A number of banks are being investigated and could face sanctions after Barclays was fined £290m ($450m) for trying to manipulate interest rates at which banks lend to each other.
Regulators in Europe, the US and Asia have said that investigations into other banks are "ongoing".
The UK's Financial Services Authority said the early signs were that Barclays had not been the only firm involved.
Barclays has said its actions "fell well short of standards".
Its traders lied to make the bank look more secure during the financial crisis and, sometimes - working with traders at other banks - to make a profit.
Chief executive Bob Diamond and three other top executives at the bank are to give up their bonuses this year.
Tracey McDermott, director of enforcement at the FSA, which imposed fines alongside the US financial regulator, told the BBC: "We have a number of investigations that are ongoing.
"Obviously we need to look at each case on its own particular facts but the initial indications are that Barclays was not the only firm that was involved in this."
The US Department of Justice also said criminal investigations into "other financial institutions and individuals" was ongoing.
Other big names believed to be under investigation include Citigroup, JP Morgan, Deutsche Bank, HSBC and Royal Bank of Scotland.
Former City minister Lord Myners told the BBC's Newsnight that any Barclays staff responsible for manipulating the Libor rate should face the prospect of going to prison.
He said the behaviour of Barclays staff was the worst he had seen.
"I think fines and public criticism will not stop these behaviours. These behaviours will not stop until the people perpetrating it or responsible for overseeing them face the prospect of criminal charges and the prospect of going to jail."
Originally posted by MidnightTide
The fun fact that 5 of the largest American banks are writing wills in case of failure, do they know something the rest of us don't?
“The prime minister says he’s really not sure we need an inquiry. How out of touch can you get?
“I have news for David Cameron: the people of this country want a moment of reckoning for our banks.
“The British people will not tolerate the establishment closing ranks saying we don’t need an inquiry. They want a light shone into every dark corner of our banking system. They want bankers held to account. They want the system rebuilt.
“Nothing less than a full public inquiry can do that. Sticking plaster solutions will not heal this wound. And nobody has confidence that the current plans of this government or the industry will be sufficient.”