North Korea on Thursday denied US accusations it was behind the WannaCry global ransomware cyberattack earlier this year and vowed to retaliate.

North Korea described the accusation as a "grave political provocation" and said Washington had "ulterior motives.”

A spokesperson from North Korea's Foreign Ministry said the allegations were "absurd," according to North Korean state news agency KCNA.

Read more: US and UK blame North Korea for WannaCry cyberattack

"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 demonizing it," the spokesperson said.

WannaCry infected some 300,000 computers in 150 countries in May, encrypting user files and demanding hundreds of dollars from their owners in exchange for the keys to get their files back.

US homeland security adviser Tom Bossert wrote a Wall Street Journal op-ed published on 18 December that claimed North Korea was directly responsible for the cyberattack.

At a press conference on Tuesday Bossert said, "After careful investigation, the United States is publicly attributing the massive WannaCry cyberattack to North Korea. We do not make this allegation lightly. We do so with evidence, and we do so with partners."

Read more: North Korea link to WannaCry ransomware 'highly likely'

"The United Kingdom, Australia, Canada, New Zealand, and Japan have seen our analysis, and they join us in denouncing North Korea for WannaCry," Bossert said.

Bossert also said Microsoft had traced the attack to cyber affiliates of the North Korean government, and others in the security community have contributed their analysis.

On Tuesday the UK came out in support of the US accusations. Foreign Office Minister Lord Ahmad said in a statement that, "The UK's National Cyber Security Centre assesses it is highly likely that North Korean actors known as the Lazarus Group were behind the WannaCry ransomware campaign – one of the most significant to hit the UK in terms of scale and disruption."

"We condemn these actions and commit ourselves to working with all responsible states to combat destructive criminal use of cyberspace. The indiscriminate use of the WannaCry ransomware demonstrates North Korean actors using their cyber programme to circumvent sanctions," Ahmad said.

Read more: New EU cyber strategy aims to cut crime and raise resilience

The cyberattack crippled hospitals, banks and other companies worldwide, including parts of the UK's National Health Service. Some companies reported massive losses, including FedEx which said they had incurred losses in the hundreds of millions of dollars.

The attack exploited a Windows vulnerability that was originally developed by the US National Security Agency, but was released in a stolen cache of NSA cyberweapons by a hacking group known as the Shadow Brokers.

law/jil (AFP, AP)