Five men have been arrested in a series of early morning raids marking the climax of a year-long investigation into international money laundering.
Three men aged 53, 37 and 20, all from London, and two others, aged 30 and 28, from East Yorkshire, are being held at their local police stations.
Wednesday's arrests are the culmination of an operation by Humberside Police's financial investigation unit.
The men in London are to be transferred to Humberside Police stations.
All of the arrests were carried out using legislation under the Proceeds of Crime Act, 2002.
A Humberside Police spokesman said the operation related to criminal activity abroad but he could not be more specific at this stage of the investigation.