Almost 4,000 cases of suspected money laundering, many of which were linked to e-money transfer providers, were reported to police in 2019, nearly triple the figure recorded the previous year, the National Police Agency (NPA) said Thursday.

The 3,913 cases reported by nonbank operators of funds transfer services compare to 1,391 in 2018, with the agency attributing the increase to the rapid expansion of e-money payment services that allow people to make transfers easily and with small service fees.

Police have become increasingly vigilant for such offenses, the agency said, suspecting crime syndicates are behind the money laundering.

An NPA report analyzed a total of 6,586 suspected money laundering cases involving e-money services between 2017 and 2019, including 1,282 reported in 2017.

Of the total, 904 involved a number of frequent money transfers made to many accounts after a large deposit, and 581 cases involved repeated transfers overseas made in a short period of time.

E-money services have been used increasingly in criminal activities in the nation. In September, NTT Docomo Inc. said more than ¥20 million ($190,000) was stolen from bank accounts linked to its e-money service.

There were 58 such operators of funds transfer services in Japan in the fiscal year through March 2018, and the number rose to 75 in fiscal 2019, which ran through March this year.