Nearly 6,000 cases of suspected money laundering linked to cryptocurrency were reported to police in the January to October period, National Police Agency officials said Thursday.

The figure is more than eight times higher than the 669 cases reported from April to December last year. Cryptocurrency exchange operators are required to report transactions suspected of involving money laundering after the law on prevention of transfer of criminal proceeds was revised in April 2017.

An NPA official attributed the rising number of reports to more operators getting used to the notification system. "We have seen some large-scale cryptocurrency thefts, and operators are believed to be scrutinizing transactions more rigorously," the official said.

In a report on the transfer of criminal proceeds released Thursday, the National Public Safety Commission pointed out the vulnerability of cryptocurrency transactions to abuse.

The commission noted cryptocurrency can be transferred overseas quickly in a highly anonymous manner as most transactions are done online.

Once cryptocurrency transactions are abused, it is difficult to track criminal proceeds as the regulations on the virtual currency are different in each country, it added.

Among suspicious transactions reported to the police, the commission's report said some users logged into their accounts from overseas even though their addresses were in Japan.

The report also said the same photo was used in identity verification documents submitted by multiple users with different names and birth dates.

In a case investigated by the police in relation to money laundering, a foreign visitor to Japan was found to have sold a cryptocurrency account ID and password.

Including all financial transactions, 346,139 suspected money laundering and other abuse cases were reported to the police in the January-October period, with most of them involving banks and other financial institutions, according to the NPA officials.