More than 50 people were arrested across Spain on Tuesday in a crackdown on boiler-room operations peddling phony investment opportunities.

Overseen by a National Court judge, the operation was carried out with cooperation from British and U.S. authorities, sources involved in the ongoing investigation told Efe.

The arrests took place in Barcelona, Madrid and Malaga.

The suspects, most of them foreign nationals, are accused of embezzlement and money laundering in the course of selling non-existent financial instruments to unwitting investors.

Many of the defrauded investors are British or U.S. citizens.

Police are searching the suspects' homes as well as the offices of several Spanish law firms thought to have been involved in the criminal scheme, the sources said. EFE