Pak Song-il, the North Korean envoy in charge of US affairs at the UN, told the Associated Press over the phone that the allegation, made by US Homeland Security adviser Tom Bossert on 19 December, was a "baseless provocation" which was being used to generate tensions.
Bossert told a briefing at the White House that after intensive investigation, the US was publicly attributing the attack to North Korea.
Pak said his country saw the claim as a US bid to create an “extremely confrontational atmosphere. If they are so sure, show us the evidence".
In making the claim, Bossert said: "We do not make this allegation lightly, we do so with evidence, we do so with partners.
"Other governments and private companies agree. The UK, Australia, Canada, New Zealand, and Japan have seen our analysis and they join us in denouncing North Korea for WannaCry."
North Korea has been accused of other cyber attacks as well, with the best known being an infiltration of Sony Pictures Entertainment after a film, The Interview, did not go down well with Pyongyang.
That allegation has also been denied by North Korea.