A tax evasion tip-off, apparently relating to Swiss bank Credit Suisse, has led to raids in five countries, including the UK,
Authorities in the Netherlands said the probe related to as many as 55,000 suspect accounts held at a Swiss bank.
Officials refused to identify which bank but Credit Suisse later released a statement to confirm its involvement in the investigation.
The coordinated raids, carried out in the Netherlands, UK, Germany, Australia and France on Thursday, followed consultations with national governments.
HM Revenue & Customs (HMRC) confirmed it was involved in the UK side of the operation which was focused, it said, on senior officials and customers of a "global financial institution".
A spokeswoman for Dutch prosecutors said millions of euros worth of goods including paintings, gold bars, cash and other assets were seized in swoops on addresses linked to 3,800 Dutch accounts.
They made two arrests at homes in The Hague and Hoofddorp.
The country's office for financial crimes prosecution (FIOD) said dozens of people were suspected of involvement in alleged fraud and money laundering through their use of bank accounts, with assets not disclosed to tax authorities.
HMRC told Sky News: "Yesterday HMRC, working with our international partners, launched a criminal investigation into suspected tax evasion and money laundering by a global financial institution and certain of its employees.
"The first phase of the investigation, which will see further, targeted, activity over the coming weeks, is focused on senior employees from within the institution, along with a number of its customers.
"The international reach of this investigation sends a clear message that there is no hiding place for those seeking to evade tax.
"Promoters and facilitators of tax evasion schemes, and their customers, need to wake up to reality and accept that attempting to hide wealth overseas, or within institutions, doesn't work and doesn't place them out of our reach."
The bank's statement read: "On 30 March 2017, Credit Suisse offices in London, Paris and Amsterdam were contacted by local authorities concerning client tax matters. We are cooperating with the authorities.
"Since 2013, Credit Suisse applies the Withholding Tax Agreement between Switzerland and the UK.
"We have implemented the Dutch and French voluntary tax disclosure programs and exited non-compliant clients.
"In addition, Credit Suisse has implemented the Automated Exchange of Information for its European locations (starting in April 2017).
"The same will apply for European individual clients served from Switzerland from 2018.
"Credit Suisse continues to follow a strategy of full client tax compliance."