Mr Browder, founder and CEO of investment fund Hermitage Capital Management, employed Russian lawyer Sergei Magnitsky, who died in Russian custody in 2009 after 11 months' incarceration. Mr Magnitsky had specialised in fraud, and his work has been linked with money laundering activities, including those which allegedly passed through the Estonian branch of Danske Bank.

A recent reportage on Swedish public broadcaster SVT alleged that Swedbank, another bank which operates in Estonia, had seen flows of at least 40 billion Swedish kronor (around €3.8 billion) between it and the Baltic units of Danske Bank, concurrent with the suspected money laundering flows via Danske in 2007-2015.

"It is my intention to file a criminal complaint against Swedbank," Browder told Reuters, declining to specify when he would file the complaint.

However, Swedbank CEO Birgitte Bonnesen told analysts late on Wednesday that Browder had told her that he would not be filing a lawsuit.

Wednesday, Swedbank's share price dropped 13.6% to 182 Swedish kronor through the course of Wednesday, in the aftermath of the SVT report.

The Swedish financial supervisory authority has said that it will cooperate in investigations of the bank's activities. Its Danish counterpart had long been involved in investigations of Danske, through which as much as €200 billion in potentially illicit funds may have transited, in conjunction with the Estonian authorities.

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