Pompeo also said that the problem has been ongoing through previous US administrations, but he argued President Donald Trump was making strides to effect change.
CIA Director Mike Pompeo said Pyongyang was moving at an "ever-alarming rate" with its weapons programme and another missile test would not be surprising.
But he rejected talk of the USA being on the "cusp of nuclear war".
But he stressed the U.S. is pursuing "a very determined diplomatic effort" led by Secretary of State Rex Tillerson that is coupled with new financial sanctions to dissuade North Korean leader Kim Jong Un from further provocations. The White House said the two "agreed North Korea must stop its provocative and escalatory behaviour".
Pompeo also said the intelligence community was not surprised by the recent news that North Korea is now capable of fitting a nuclear warhead on a missile.
Following Trump's initial threat, North Korea threatened to target the tiny Pacific island of Guam, a US territory that is home to large USA air and naval bases.
President Trump wrote on Twitter on Friday that U.S.
Rodong Sinmun, North Korea's official newspaper, said the volunteers had offered to join or rejoin the People's Army after the Korea Central News Agency (KCNA) issued a statement on Monday condemning new sanctions imposed by the United Nations in retaliation for North Korean missile tests.
Pompeo's remarks came on Sunday, capping a week in which US President Donald Trump vowed "fire and fury" if North Korea continued to threaten the United States with nuclear weapons, and Pyongyang countered by announcing plans to test-launch missiles toward Guam.
North Korea, for its part, threatened to shoot four missiles towards the island of Guam, a strategic outpost of the u.s. forces in the Pacific, where are stationed about 6,000 american soldiers.