"The capability that they've delivered and demonstrated the other day we assess could reach the United States," Aquilino said during a discussion hosted by the Aspen Institute on Tuesday.
Aquilino said the United States is still reviewing North Korea's nuclear capability.
Earlier in the day, media reported that North Korea fired two possible ballistic missiles. According to sources, the projectiles likely fell into the Sea of Japan but outside of Japan's exclusive economic zone.
The broadcaster added that missiles flew 550-600 kilometers (340-370 miles), reaching an altitude of 50 kilometers.