A leaked set of U.S. government documents suggests some of the biggest names in global banking were involved in moving dirty money around the world, in some cases for criminals.

The so-called FinCEN files include more than 2,500 documents, most of which were sent to U.S. authorities by banks to highlight potentially shady activity.

They include suspicious activity reports or SARs, which lenders use to notify authorities of potentially shady activity, such as money laundering, terror financing, corruption, fraud and sanctions violations.

In total, the documents - which were obtained by BuzzFeed News and shared with the International Consortium of Investigative Journalists (ICIJ) - showed more than $2 trillion of transactions took place between 1999 and 2017.

In some cases, transactions were carried out by Western banks even after U.S. authorities fined them for previous failures in stopping the flow of illicit funds, according to the ICIJ.

Five of the world's largest lenders appeared most often in the leaked files, including HSBC, JP Morgan, Standard Chartered, Bank of New York Mellon and Deutsche Bank.

"We are taking the fight against money laundering and against the flight of capital very, very seriously," said Joerg Eigendorf, a spokesman for Deutsche Bank. "We are closely cooperating with criminal investigation authorities, just like other banks. What's being reported now is not new, not to us and not to our supervisory authority. Everything has been processed and we had a very close look at everything," he added.

In a statement to Reuters, HSBC also said the information was "historical" and that since 2012, it's "embarked on a multi-year journey to overhaul its ability to combat financial crime."

Standard Chartered said it takes its "responsibility to fight financial crime extremely seriously" and has "invested substantially in its compliance programs."

American bank JP Morgan said it has devoted "thousands of employees and hundreds of millions of dollars" to help fight financial crime, while BNY Mellon said: "We fully comply with all applicable laws and regulations”.

The leaked files came from the U.S. Department of Treasury's Financial Crimes Enforcement Network, also known as FinCen.

It said the "unauthorized disclosure of SARs is a crime that can impact the national security of the United States.”

The leak also raises awkward questions for the UK's role in global banking, with London described as a weak link in the international financial system.

More than 3,000 UK companies were named in the FinCEN files, more than any other country.