“There was a test,” Patrick Shanahan, the acting defense secretary, told reporters as he met his Albanian counterpart at the Pentagon.
He declined to elaborate on the findings of US intelligence but said, “It’s not a ballistic missile.”
“Also there’s no change to our posture or to our operations,” he said.
North Korean state media earlier announced that leader Kim Jong Un had supervised the test-firing of a new tactical weapon with a “powerful warhead,” hailing what it called a contribution of “very weighty significance” to its arsenal.
Analysts have speculated that the test could have involved anything from a small anti-tank missile to relatively routine artillery, with a South Korean official also saying that the country saw no sign of a ballistic missile.
US President Donald Trump has repeatedly boasted that North Korea has suspended both missile and nuclear tests since he embarked on diplomacy a year ago to ease soaring tensions.
Trump has met twice with Kim but their second summit, held in Hanoi in February, ended in deadlock with the United States insisting on full denuclearization before it eases sanctions.
Amid a standstill in talks, North Korea on Thursday both announced the test and demanded that Secretary of State Mike Pompeo be excluded from negotiations after he apparently encouraged Trump to stand firm in Hanoi.