A WhatsApp group chat was allegedly used to coordinate the transfer of hundreds of millions of euros in cash around the world, with some transactions linked to organised crime and extremist activity, according to an investigation by European broadcasters.

The group, called “Traders of Greater Europe”, had 532 members who used the chat to arrange cross-border cash transfers for clients. The network reportedly operated across numerous countries and included transfers involving British cities such as Birmingham and London.

Investigators found that in one case, payments originating in Brussels were sent to militants associated with the Islamic State group in Syria.

The investigation by the European Broadcasting Union’s investigative journalism network, which includes the BBC, also uncovered evidence that similar informal cash-transfer systems were being used in criminal activities including people smuggling and drug trafficking.

More than 82,000 messages were sent in the WhatsApp group between late February and December 2022. The chat was initially uncovered by Belgian investigating magistrate Vincent Guerra while examining suspected terror financing.

Guerra described the volume of transactions as “staggering” and said the network appeared to operate across the globe.

What began as an investigation focused on terrorism financing ultimately revealed a much larger flow of transactions, according to Guerra, with the original case representing only a small part of the network’s overall financial activity.

The investigation highlights the challenges authorities face in tracking informal international cash-transfer networks that can operate with limited conventional financial records.