HANOI, June 5 (Xinhua) -- Vietnam imported over 6,300 rigs, or application-specific integrated circuit devices used to mine digital currencies such as Bitcoin and Ethereum, in the first four months of this year, according to the General Department of Vietnam Customs on Tuesday.

Last year, more than 9,300 rigs were imported into Vietnam, most of which went to Ho Chi Minh City and Hanoi capital, the department said.

Cryptocurrency mining is not banned in Vietnam, but using cryptocurrencies as means of payment is prohibited, so trading them is very risky, according to local officials and digital currency miners and traders.

To prevent fraudulent activities concerning cryptocurrencies, Vietnam's Finance Ministry is proposing a temporary ban on importing rigs.

In April, Vietnamese Prime Minister Nguyen Xuan Phuc signed a directive calling for stronger measures to rein in cryptocurrencies. Under the directive, credit institutions in Vietnam are not allowed to carry out cryptocurrency-related transactions and must swiftly report any suspicious activities.

Public companies, brokerages, fund management companies and investment funds are banned from any illegal activities related to cryptocurrencies and are required to comply with anti-money laundering rules.