North Koreawas behind the WannaCry attack which crippled the NHS after stealing US cyber weapons,the head of Microsoft has claimed.

The cyber attack in May was the largest in the NHS's history and put lives under threat as hundreds of operations were cancelled.

It led to ambulances being diverted after 40 hospital trusts became infected by a “ransomware” attack demanding payment to regain access to vital medical records.

Now the President of Microsoft has told ITV News that the government of North Korea was responsible for the attack.

Brad Smith said he believed "with great confidence" that Pyongyang was behind the hack which impacted 200,000 computers in 150 countries around the world.

"I think at this point that all observers in the know have concluded that WannaCry was caused by North Korea using cyber tools or weapons that were stolen from the National Security Agency in the United States," he said.

North Korea has been widely linked with the WannaCry cyber-attack but this is the first time that an executive at Microsoft has blamed the administration publicly.

Mr Smith says cyber-attacks by nation-states have become more frequent and more severe: "I think over last six months we've seen threats come to life, unfortunately, in new and more serious way. The problem has become bigger"