North Korea tested three intercontinental ballistic missiles in 2017, as well as its sixth nuclear weapon.
CIA director Mike Pompeo revealed intelligence officials had seen the tests coming, but had difficulty predicting the exact moment dictator Kim Jong-un would ramp up his programme.
He told reporters: “We can always identify that the program is continuing.
“We’ll never know the exact nature of what’s taking place. We’ll never know the exact moment that they’re going to continue.
“But the core risk that the policymakers needed to know was that North Korea’s nuclear weapons program is continuing to expand, advance, become more powerful, more capable, more reliable.”