0600 GMT March 22, 2018
Harris made the remarks during a speech before a think tank in Tokyo on Wednesday after meeting with Japanese leaders.
On Sunday, North Korea test-launched an intermediate-range ballistic missile from the northwestern city of Kusong that many experts believe could be its most advanced yet. The missile flew some 700km (435 miles), reaching an altitude of 2,000km and landing in the sea west of Japan.
The missile, which the North’s media said can carry a heavy nuclear warhead, could reach the US state of Hawaii if it was fired on a normal trajectory, American experts warn.
"Combining nuclear warheads with ballistic technology in the hands of a volatile leader like Kim Jong-un is a recipe for a disaster," Harris said.
"Kim Jong-un is not afraid to fail in public and every test he makes is a success because it takes North Korea one step closer to being able to deliver a nuclear-equipped missile anywhere in the world," the top officer added.
While in Tokyo, Harris met Japan's Prime Minister Shinzo Abe, Foreign Minister Fumio Kishida and Defense Minister Tomomi Inada for talks that focused primarily on North Korea’s missile and nuclear programs.
"The actions of North Korea are unacceptable to the world, really," the admiral said during discussions with Kishida. "It underscores not only the importance of the US-Japan alliance, but also the US, Japan and South Korea trilateral co-operation."
On Tuesday, US Ambassador to the United Nations Nikki Haley accused North Korea of threatening the entire world with its military actions.
Speaking to reporters ahead of an emergency meeting of the UN Security Council, Haley vowed to "call out" countries that support Pyongyang and its nuclear ambitions.
"If you are a country that is supplying or supporting North Korea, we will call you out on it. We will make sure that everyone knows who you are and we will target those sanctions towards you as well," she told reporters.
The Security Council on Monday condemned the North's latest missile test and warned of new sanctions.
Haley also said that the United States would consider dialog with Pyongyang only if it stopped all nuclear and ballistic missile tests.
North Korea has repeatedly said it would not abandon its missile and nuclear programs unless the US ended its hostility toward the country.