(Bloomberg) -- UK finance investigators arrested three London-based individuals on suspicion of insider dealing and money laundering, ramping up investigations into possible links to organized crime.

The Financial Conduct Authority said Wednesday it conducted a “major operation” alongside police over two days in February and interviewed four suspects, one of whom wasn’t arrested. The regulator said digital devices were seized from London residences. 

The announcement came at the same time as the FCA warned in a separate notice that trading by organized crime forms a “significant component” of the suspicious trading activity it sees in equity markets.

“Insider dealing poses a significant threat to the integrity of financial markets both in the UK and overseas. The FCA is committed to combating organized criminal networks involved in this threat,” said Steve Smart, the FCA’s new enforcement director. Smart previously worked at the National Crime Agency, which assisted the FCA with the operation.

In the notice, the FCA warned that mergers and acquisitions advisory firms should be alert to dealmakers being approached by members of gangs. The watchdog warned that it was “likely” that junior members of staff were being targeted and that firms should limit their social media references around deals.

The FCA said it considered suspicious trading in equity spread betting and contracts-for-difference around M&A deals to be characteristic of the activity of organized crime groups.

(Updates with detail from FCA’s notice in final paragraph.)

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