There was no definitive confirmation that Credit Suisse was the main target of the fraud investigations, run by at least four European countries and Canberra and apparently involving hundreds of suspects.
The Swiss financial giant simply confirmed that its offices in London, Paris and Amsterdam had been visited by local authorities on Thursday “concerning client tax matters”.
“We are cooperating with the authorities”, Switzerland's number-two bank said in a statement.
Dutch prosecutors said dozens of people who allegedly concealed millions of euros were being probed for tax fraud and money laundering and that records were seized on Thursday from “a Swiss bank” which they did not name.
Similar operations were carried out in Britain, France, Germany and Australia, all focused on clients who “deposited their money in the same Swiss bank”, according to a statement from the National Prosecutor's Office for Serious Fraud, Environmental Crime and Asset Confiscation (FIOD).
Two people accused of not declaring their savings have been arrested and two other suspects were interrogated, the FIOD said.
“Properties, and jewellery, an expensive car, expensive paintings and a gold bar”, were seized from houses in The Hague and three other areas, the Dutch statement added.
'Senior employees' targeted
Britain's Revenue and Customs office said that it on Thursday along with international partners had launched a criminal probe into tax evasion and money laundering “by a global financial institution”.
“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 statement from London said.
It also made no mention of Credit Suisse, but said the investigation should serve as a stark reminder to institutions that aim to help clients evade tax.
Would-be tax cheats “need to wake up to reality and accept that attempting to hide wealth overseas, or within institutions, doesn't work.”
French prosecutors confirmed that they too had opened a tax fraud investigation into undeclared Swiss bank accounts.
The financial fraud office said it had identified several thousands of accounts in Switzerland that were allegedly used to hide money.
This amounted to suspected “aggravated dissimulation of tax fraud”, it said, with no reference to Credit Suisse.
346 people implicated
In Australia, revenue and financial services minister Kelly O'Dwyer said investigators there had identified more than 346 people “with links to Swiss banking relationship managers” who allegedly promoted tax evasion.
Australian investigators plan to “move quickly” against those who schemed to hide wealth, she said, noting however that some of those in the firing line will likely be exonerated.
The launch of a coordinated, international probe targeting an iconic Swiss bank came as a surprise to Bern, Switzerland's ATS news agency reported.
The Swiss attorney general's office was not aware of the operations and demanded a written explanation from Dutch officials in particular over the lack of cooperation, according to ATS.
Credit Suisse has previously been in the crosshairs of tax officials.
US regulators fined the bank $2.6 billion (2.4 billion euros) in 2014 for helping Americans evade taxes.
“Credit Suisse continues to follow a strategy of full client tax compliance,” the bank said on Friday.
The coordinated probe comes as Credit Suisse rolls out its new Automatic Exchange of Information programme designed to share taxpayer information with relevant global authorities as part of a wider Swiss crackdown on money laundering and secretive banking.