US authorities are sounding the alarm over North Korea's cyber activities, warning that the rogue state poses a "significant threat" to the integrity and stability of the international financial system.

In a joint alert warning, the FBI, along with the Departments of State, Homeland Security, and Treasury, accuse North Korea of using cybercrime to fund its weapons of mass destruction and ballistic missile programmes.

A UN report last year estimated that the country has generated an estimated $2 billion in revenues for its weapons programme through the state-sponsored looting of financial institutions and cryptocurrency exchanges.

The new US alert lists a host of acts believed to have been carried out by the North Koreans, including the 2016 Bangladesh Bank heist, the WannaCry ransomware campaign, the FASTCash ATM cashout scam, and a $250 million digital currency exchange hack.

To help tackle the threat, the US is calling for raised awareness about North Korea's actions, the sharing between countries of technical information of the threat, and the strengthening of AML and terrorism financing rules compliance.

Meanwhile, the State department is offering a reward of up to $5 million to anyone with information about illicit North Korea activities in cyberspace.

"It is vital for the international community, network defenders, and the public to stay vigilant and to work together to mitigate the cyber threat posed by North Korea," says the alert.