Baik Tae-hyun, spokesman of South Korea's Unification Ministry, which deals with matters related to North Korea, said Monday that the Seoul government was examining whether the North was behind hacking attacks on a cryptocurrency exchange in June.
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.
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.
Bossert said the Trump administration will continue to use its "maximum pressure strategy to curb Pyongyang's ability to mount attacks, cyber or otherwise".
It battered Britain's National Health Service, where the cyberattack froze computers at hospitals across the country, closing emergency rooms and bringing medical treatment to a halt.
South Korean and United States officials have accused the North of launching a slew of cyberattacks in recent years.
Palestinian girl filmed hitting Israeli soldiers detained
Villagers were denied access to the spring that provided for their community for as long as anyone could remember. Mohammad had to be put under a medically induced coma , from which he woke up on Tuesday, 72 hours later.
The missile launch defied global sanctions on the country led by dictator Kim Jong Un, and it drew ire across the globe, as this was the highest missile North Korea has ever launched - reaching almost 2,800 miles at its highest.
Thursday's warning came amid heightened tensions following the North's test-launch of its most powerful missile last month. Among them is a U.S. accusation that it hacked Sony Pictures in 2014 over the movie The Interview, a satirical film about a plot to assassinate North Korean leader Kim Jong Un.
Defense Secretary Jim Mattis said the missile test went "higher, frankly, than any previous shot they have taken", and that North Korea can hit "everywhere in the world, basically".
Security firm FireEye believes United States sanctions against North Korea are fueling its interest in Bitcoin and cryptocurrencies.