Sources familiar with the matter say the justice department could bring its first criminal charges early next year, and that Lawsky could take action against banks under his jurisdiction before his expected departure, which may come early next year.

Wednesday's deal appears to be the tip of the iceberg when it comes to further legal action, said Josh Rosner, managing director of Graham Fisher, a research consultancy. "Did they let anyone off of criminal liability? What was settled?" he said.

Former prosecutors also said criminal authorities have extensive evidence, based upon transcripts released by Britain's Financial Conduct Authority and US civil authorities of traders brazenly discussing attempts to manipulate foreign exchange rates.

"Recordings are typically the strongest evidence you can have," one former prosecutor said.

Another former prosecutor familiar with the probes said he expected that the publicity around the first round of settlements would add momentum to the outstanding investigations.

It is unclear how much higher the settlement amounts will go beyond the US$4.3 billion, and which banks will move first in settling, especially with the justice department. Earlier this month JP Morgan said it was in talks with the department to resolve its investigation, one of the strongest such disclosures, suggesting it could be one of the first to settle criminal charges.

The banks also face a criminal probe from Britain's Serious Fraud Office, and interest from the European Commission, which has not yet opened a formal investigation.

Lawsky, the head of New York's Department of Financial Services, has in recent months helped land record settlements from banks on sanctions and tax-related violations, and could significantly drive up the ultimate price tag on the foreign exchange probes.

Not only can he threaten some of the banks' licences, but he also has been known to demand firings of employees and clawbacks of their bonuses.

In Lawsky's probe, more than a dozen banks have been asked for documents, including Barclays, Credit Suisse, Deutsche Bank, Goldman Sachs, Lloyds Banking Group, Societe Generale and Standard Chartered. In a sign of Lawsky's clout, Barclays pulled out of Wednesday's coordinated deal because it did not want to settle with other regulators without having come to an agreement with Lawsky, two sources said.

Lawsky has already installed a monitor from advisory firm Devon Capital at Barclays and is close to installing one at Deutsche Bank - a move that will allow him to collect greater evidence of alleged manipulation and could strengthen his hand in settlement talks, sources said.

Sources familiar with the justice department's criminal probe said banks could face a level of penalties more severe than those levied against them in a separate investigation into the rigging of the London interbank offer rate, a benchmark known as Libor.

The justice department is also expected to pursue criminal charges against individuals. Sources have said that prosecutors are likely to bring charges against traders and their supervisors, but are not likely to reach senior executives at any of the banks.

In private chat-room transcripts released on Wednesday, traders are seen working together to move rates at which currency pairs like the US dollar and the British pound trade, and to cover their tracks.

One Citigroup trader, for example, asks a trader at UBS about another trader who may join the chat room: "Is he gonna protect us … like we protect each other against our own branches."

In another chat, an HSBC trader and others celebrate moving the rate: "Well done gents," one said. "Hooray nice team work," another responds.