North Korea on Thursday denied US accusations it was behind the WannaCry global ransomware cyberattack, saying Washington was demonising it. WannaCry infected some 300,000 computers in 150 nations in May, encrypting user files and demanding hundreds of dollars from their owners for the keys to get them back. The White House this week blamed Pyongyang for it, adding its voice to several other countries that had already done so. A spokesman for Pyongyang's foreign ministry said the US allegations were "absurd", adding: "As we have clearly stated on several occasions, we have nothing to do with cyber-attacks." Washington had "ulterior" motives, the spokesman added according to the North's KCNA news agency. "This move is a grave political provocation by the US aimed at inducing the international society into a confrontation against the DPRK by tarnishing the image of the dignified country and demonising it," he said. North Korea is subject to multiple United Nations sanctions over its banned nuclear and ballistic missile programmes, and tested its third ICBM last month. Leader Kim Jong-Un declared his country had achieved full nuclear statehood, in a challenge to US President Donald Trump who responded with promises of "major sanctions". According to experts North Korea's cyberwarfare targets have expanded from the political -- it was accused of hacking into Sony Pictures Entertainment in 2014 to take revenge for "The Interview", a satirical film that mocked Kim -- to the financial, as it seeks new sources of funding. A South Korean cryptocurrency exchange shut down on Tuesday after losing 17 percent of its assets in a hacking -- its second cyberattack this year, with the North accused of involvement in the first. Investigators are probing the possibility that Pyongyang was also behind Tuesday's incident, the Wall Street Journal and Bloomberg News reported. The North is blamed for a massive $81 million cyber-heist from the Bangladesh Central Bank (BCB) in 2016, as well as the theft of $60 million from Taiwan's Far Eastern International Bank in October. Pyongyang has angrily denied the accusations -- which it described as a "slander" against the authorities -- but analysts say the digital footprints left behind suggest otherwise.