"North Korea's claims may be hyperbolic, but as to the policy of the United States, there should be no doubt: We will draw upon the full range of our capabilities to protect against, and respond to, the threat posed to us and our allies by North Korea," he said.
Concern over 'bellicose rhetoric'
In Washington, White House Press Secretary Jay Carney told reporters that Pyongyang's "bellicose rhetoric" had raised concerns. "The DPRK will achieve nothing by threats or provocations, which will only further isolate North Korea and undermine international efforts to ensure peace and stability in northeast Asia," he said.
Also Monday, North Korea did not answer its hotline with Seoul, South Korea's Unification Ministry said, according to the Yonhap news agency.
The ministry said the North did not answer two attempts to communicate by telephone at 9 a.m. and 4 p.m. local time.
The military hotline was set up in 2004 with the goal of easing tensions along the heavily fortified border between South and North, the world's last Cold War frontier.
Last week, Pyongyang said it planned to terminate its military telephone line with the United States.
But Andre Kok, deputy public affairs officer for U.S. Forces in Korea, said reports that the North's Korean People's Army, known as the KPA, cut off communication often arise when military training exercises are taking place.
"When we place a call on the direct phone line and the KPA does not answer, we have no way of knowing if the KPA has actually disconnected the phone lines or are just not answering the phone," he said.
North Korea's nuclear warning
North Korea had previously warned it could carry out strikes against the United States and South Korea.
But analysts say North Korea is years away from having the technology needed to mount a nuclear warhead on a missile and aim it accurately at a target.
And, analysts say, North Korea is unlikely to seek a direct military conflict with the United States, preferring instead to try to gain traction through threats and the buildup of its military deterrent.
Its problems are also internal: a U.N. Human Rights Council report dated February 1 cited "grave, systematic and widespread violations of human rights" in the country.
The Koreas are still technically at war because the 1950-53 war ended in a truce, not a peace treaty.
In 2002, then-U.S. President George W. Bush labeled Pyongyang part of an "axis of evil" with Iraq and Iran.