The UK's Financial Conduct Authority (FCA) has taken another step in its crackdown on illegal cryptocurrency cash machines.

The FCA joined forces with Exeter, Nottingham and Sheffield police to carry out inspections in the area. The regulator said in an announcement on Friday that the devices, which convert fiat money into cryptocurrencies, pose a money laundering threat and are not registered with the FCA as required by law.

"It is illegal to operate a cryptocurrency cash machine that is not registered with the FCA," said Therese Chambers, the FCA's enforcement and markets regulation executive. "To stop illegal activity, we will take action."

The regulator said it had been reviewing the evidence obtained from the audit, but did not elaborate on what further action it might take.

According to the CoinATMRadar website, there are 17 cryptocurrency ATMs in the UK. But the FCA says there are about 40 cryptocurrency firms that are not authorized to provide services.

In February, the FCA, in collaboration with West Yorkshire Police, launched an investigation into suspected illegal cryptocurrency cash machines operating around Leeds.