He reiterated that the nation's "nuclear weapons and missile programs pose a serious threat to the United States and to the security environment in East Asia."
North Korea denied responsibility in a wave of cyberattacks on tens of thousands of computers at South Korean banks and broadcasters last month, the North's state news agency, KCNA, reported Friday.
South Korea this week accused the North of carrying out the March 20 attacks. An official South Korean investigation found that many of the malignant codes employed in the attacks were similar to ones used previously by the North, said Lee Seung-won, an official at the South Korean science ministry.
A spokesman for the General Staff of the Korean People's Army said the allegations are "groundless" and "a deliberate provocation to push the situation on the Korean Peninsula to an extreme phase," according to KCNA.
Friday, North Korea also issued a scathing warning to Japan, saying via KCNA that Tokyo should "stop recklessly working for staging a comeback on Korea, depending on its American master."
Japanese foreign minister spokesman Masaru Sato said such remarks only hurt North Korea.
"Japan would not be pushed around by rhetoric of North Korea," he said.
Late Friday, Japan's Transport Ministry issued a notice requiring Japanese airplanes to report to the U.S. military if they fly near the U.S. military's Kadena base in Okinawa prefecture, the Kyodo News Agency said.
The notice, made at the request of the U.S. military in Japan, is believed to be part of precautions taken against possible North Korean missile launches.
It concerns the airspace within 30 kilometers (about 19 miles) of the base in southern Japan, where Patriot missiles are deployed.
North Korea began to sharpen its threats in February, after the United Nations reacted to the country's third nuclear test with tougher sanctions. Annual military exercises involving U.S. and South Korean troops have added to the tensions.
At the Thursday House Intelligence Committee hearing, Clapper said the United States believed the primary objective of Kim's bellicose rhetoric was to "consolidate and affirm his power."
Earlier in the crisis, the United States drew attention to shows of strength, such as practice missions by B-2 stealth bombers.
Kerry said Friday that U.S. officials were working to calm the crisis, noting President Barack Obama had canceled some of the exercises.
"I think we have lowered our rhetoric significantly," Kerry said.