The European commission has described the €200bn (£178bn) money-laundering case at Denmark’s largest bank as “the biggest scandal” in Europe.

Věra Jourová, the European commissioner for justice, said she would summon ministers from Denmark and Estonia to explain how Danske Bank executives and regulators missed the scandal.

“I want to understand better where the main errors happened, whether it was purely a fault of the due diligence done by the bank itself or whether there was some mistake of the supervisory authority,” Jourová told reporters on Thursday.

Danske bank chief resigns over €200bn money-laundering scandal Read more

She added: “This is the biggest scandal, which we have now in Europe, which is also a very unpleasant lesson [showing] the need to be much more vigilant and [for] much more prudent checking [of banks’ activities].”

Denmark’s prime minister also expressed his shock at the scale of the scandal, describing it as “frankly quite horrible” as he vowed to take further action against Danske Bank and its executives.

Lars Løkke Rasmussen said he was outraged at the scale of the money-laundering operation at Danske’s Estonian branch. An independent investigation published on Wednesday found that 15,000 customers were involved in suspicious transactions.

“The fact that Denmark has been at the centre of a money laundering of this size is frankly quite horrible,” Rasmussen told reporters at the European Union meeting in Salzburg. The bank’s chief executive Thomas Borgen resigned on Wednesday but Rasmussen said: “The case does not end with this.”

The Danish regulator financial regulator said it had reopened its investigation into the bank. “We’re reopening the investigation of the bank that we initially closed in May,” Jesper Berg, the head of Denmark’s Financial Supervisory Authority (FSA) told the Danish broadcaster TV 2 on Thursday. “When new information comes to light, then we will always see if there is more to come. We have been following the case since May. But now the work we have in this matter intensifies.”

Earlier this week Danish politicians voted through an eight-fold increase in the maximum fines for money laundering – making it one of the toughest jurisdictions in Europe. However, the new legislation will not be retrospective and will therefore not cover the Danske Bank Estonian money laundering, which took place between 2007 and 2015.

Denmark’s business minister, Rasmus Jarlov, said he expected that Danish authorities could fine Danske 4bn Danish kroner (£475m). Analysts expect Danske to be fined billions of dollars by Danish, European and US regulators. The bank on Wednesday said it would donate 1.5bn kroner to a charity focused on “combating international financial crime”.

Jarlov said: “We’re aware that foreign authorities are monitoring Danish banks and could open cases. But that just makes it even more important that we handle things thoroughly in Denmark, to make sure nobody elsewhere is left with the impression that we’re not coming down severely on this.”

Jeppe Kofod, a Danish member of the European parliament and a member of the parliament’s special committee on financial crimes, tax evasion and tax avoidance., said US authorities were examining the case and he expected a full investigation.

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“I was in the US in July and spoke with the Treasury Department and there is no doubt that they also follow the Danske Bank case closely,” he told Bloomberg. “This case is far from finished, it has just begun.”

Bill Browder, a US hedge fund manager who has been leading a crusade against corruption and money laundering by rich and powerful Russians, has claimed that Danske’s Estonian branch was involved in the fraud uncovered by his lawyer Sergei Magnitsky, who was beaten to death in a Russia jail.

Danske’s shares, which have lost 28% of their value so far this year, rose 4.5% on Thursday after UBS advised clients to buy the shares. “The 87-page report on the non-resident portfolio contained a number of positives in our view,” Johan Ekblom, a UBS analyst said in a note referring to the lack of a formal US investigation. “We think Danske Bank shares look attractive, even in a scenario of material financial fines.”