According to investigative SVT program Uppdrag Granskning, at least 40 billion Swedish kronor ( around €3.8 billion) moved between Swedbank and the Baltic units of Danske Bank, over around a 10 year period.

Most of the transfers took place during the period 2007-2015, the same time frame that as much as €200 billion in potentially illicit funds, mostly of Russian Federation origin, are thought to have passed through Danske Estonia.

The Swedbank flows concern around 50 customers, most of which are shell companies and corporate customers who had no business activities, the SVT broadcast said.

Estonian daily Postimees has additional information about the connection between over 10 Estonian customers at Swedbank and the same suspicious cash flows. The sum of transactions that moved via their accounts amounted to as much as millions, or sometimes tens of millions, of dollars, the paper says.

Swedbank issues statement

Swedbank Estonia representatives have refused to meet with Postimees journalists to discuss the issue, with head of communications Kristiina Herodes only forwarding a general written comment in response to the paper's requests.

"We do not tolerate money laundering and consider it a very serious crime,'' the statement read.

''In banking today, this is certainly one of the most complex challenges we are fighting against. In order to launder money received illegally, attempts are made, by constantly inventing new ways, to use financial institutions and this is why we put a strong emphasis on prevention. This is a priority for us," the statement continued, according to BNS.

SVT's investigation also revealed that part of the Swedbank flows were related to the Russian lawyer Sergei Magnitsky, a corruption specialist who in 2007 died after 11 months' incarceration by Russian authorities. Mr Magnitsky's former employer, British-American investor Bill Browder, has been instrumental in revealing the scale of the Danske and related, potentially laundered money flows.

Following the news, Swedbank's share price fell by 5.64% slightly before 11.00 EET, BNS reports, amid fears that if money laundering activities are proven, the bank will be landed with a substantial fine in the US.

Other banks previously investigated in relation to Danske Estonia include Deutsche Bank. The German bank has since not been found to have engaged in any wrong-doing.

On Tuesday, the Estonian Financial Supervisory Authority announced that the Estonian branch of Danske was to be closed within eight months.

Swedbank is one of the largest high street banks in Estonia, with a reported €207 million profit in 2018.