It flowed in "substantial" chunks from firms in Estonia and Lithuania which conducted no known business and which ought to have set off anti-money laundering alarm bells, he added.

"Any decent due diligence would have caught this stuff ... There's strong suspicion of money laundering there based on this information, and we're asking law enforcement to investigate," Browder told the Bloomberg news agency.

"Every time you pull on some strings to open a case, it leads us to other potential perpetrators," he told the Financial Times, after having uncovered the new Nordea information via ongoing cases into the Magnitsky affair in France and Lithuania.

Browder used to run a hedge fund in Russia, but has spent the past 10 years campaigning for tougher Western sanctions in Magnitsky's name.

He has also uncovered illicit Russian funds in Austria, Cyprus, Germany, and the UK related to a $230m Russian fraud perpetrated by a group of corrupt officials and mafia enforcers with links to the highest level of the Kremlin.

The Nordea complaint comes after Browder showed Danish lender Danske Bank had handled illicit Russian money.

The Danske Bank case blew up into the biggest money-laundering scandal in EU history when the bank admitted to having handled up to €200bn of suspicious Russia money.

It also prompted the European Commission to seek new anti-money laundering powers for the European Banking Authority, an EU agency.

For its part, Nordea, which has its HQ in Helsinki, said during recent years it had "invested heavily in strengthening its resources to counter money-laundering and other forms of financial crime across all countries where we operate."

"To combat financial crime, it's part of our daily operations to continuously review customer activity. In any cases where we deem it to be suspicious transactions, we report it to the authorities for them to take forward," it also said.

"It's clear there was something deeply bent going on inside Danske Bank," Browder told Bloomberg.

"We don't know enough yet to make any conclusions about Nordea, which is one of the reasons" for asking prosecutors to open cases, he said.