They have also launched a criminal probe into 45 people suspected of involvement in the operation.

The activity was first unearthed by police in the central province of Ha Tinh in May. The gang was found running two online rings with a total of 1,566 accounts, Colonel Vo Trong Hai, Director of Ha Tinh Police Department, told local media on Tuesday. One third of these accounts belonged to betters, while the remaining were admin accounts.

A large-scale investigation was launched by police under the Ministry of Public Security in collaboration with police in the five localities of Ha Tinh, Khanh Hoa, Binh Dinh, Phu Yen and Ho Chi Minh City.

On May 26, the authorities arrested 11 people, including Le Canh Bao, 43, of Khanh Hoa, believed to be the kingpin of the two rings. He had assigned Pham Hai, 42, and Ho Xuan Dat, 28, to manage the accounts.

Five days later, a criminal probe was launched into the case and more details about the ring were revealed.

The ring had been operated for seven months, from October last year to May this year, collecting an average of VND500 billion ($21.6 million) of betting money every month. At the time they were busted, the total value of these transactions were estimated at VND3 trillion ($130 million).

Of the 45 people being investigated, 29 are gambling organizers and 16 are gamblers.

Vietnam has considerably relaxed its stance on gambling as a "social evil," legalizing sports betting in 2017 and allowing, on a pilot basis, people aged over 21 with a monthly income of at least VND10 million ($432) to play in a casino on the southern Phu Quoc Island.

But all other forms of gambling remain illegal.