But Locklear told the Senate Armed Services Committee that he was confident that the U.S. military can thwart North Korea if it chooses to act. He made clear that any U.S. decision would be contingent on where the missile is headed, information that the U.S. could ascertain fairly quickly.
"Do we have the capability to intercept a missile if the North Koreans launch within the next several days?" Sen. John McCain, R-Ariz., asked the admiral.
"We do," Locklear answered.
He said North Korea is keeping a large percentage of its combat forces along the demilitarized zone with South Korea, a position that allows the North to threaten U.S. and South Korean civilian and military personnel.
McCain said the saber-rattling of today struck him as the greatest tension between North Korea, South Korea and the U.S. since the end of the Korean War in the early 1950s.
"I would agree that in my recollection I don't know a greater time," the 58-year-old Locklear said.
Increasingly bellicose rhetoric has come from Pyongyang and its leader, with North Korea urging foreign companies and tourists to leave South Korea and warning that the countries are on the verge of a nuclear war.
At the White House, spokesman Jay Carney brushed off the North's declaration that nuclear war was imminent as "more unhelpful rhetoric" and part of a pattern of combative statements and behavior that Pyongyang's leadership has demonstrated for years. He said the U.S. was working with Seoul and Tokyo on the issue.
"It is unhelpful, it is concerning, it is provocative," Carney said.
Senate Armed Services Committee Chairman Carl Levin, D-Mich., told Locklear that the North Korean government's threats "appear to exceed its capabilities, and its use of what capabilities it has against the U.S. or our allies seems highly unlikely and would be completely contrary to the regime's primary goal of survival."
"Nonetheless, its words and actions are not without consequences," Levin said.
The Democrat questioned the Obama administration's decision to delay a long-scheduled operational test of an intercontinental ballistic missile amid the North Korea rhetoric.
Locklear said he agreed with the decision to delay the test.
"We have demonstrated to the people of the region, demonstrated to the leadership of North Korea, our ability and willingness to defend our nation, our people, our allies and our forward deployed forces," Locklear said, citing other steps the U.S. military has taken in recent weeks.
The U.S. has moved two of the Navy's missile-defense ships closer to the Korean peninsula, and a land-based system is being deployed to the Pacific territory of Guam. The U.S. also called attention to the annual U.S.-South Korean military exercise that included a practice run over South Korea by B-2 stealth bombers.
Levin mentioned that President Barack Obama recently talked to China's new president, Xi Jinping, about the U.S. efforts to deal with North Korea. Locklear said he has not had similar conversations with his Chinese counterparts.
In an exchange with Sen. Angus King, I-Maine, Locklear acknowledged a hotline connection between Washington and Beijing similar to what existed with Moscow during the Cold War, and said both sides need to move forward in continuing conversations.
Locklear told Levin that he would explore the possibility of making direct contact with his military counterparts in China and communicate with them the seriousness of the situation on the Korean peninsula.
Sen. Tim Kaine, D-Va., insisted that North Korea's nuclear program could come to a "grinding halt" if China pressured Pyongyang.
Reflecting the uneasy relationship, Sen. Lindsey Graham, R-S.C., asked Locklear if he considers China a "friend or a foe." Locklear said neither.
"I consider (China), at this point in time, someone we have to develop a strategic partnership with to manage competition between two world powers," Locklear said.
Locklear said Kim Jong Un has adopted pages from the playbook used by his father, Kim Jong Il, but his approach differs in a significant way. Kim Jong Un's father, as well as his grandfather, Kim Il Sung, made sure they had "off ramps" that gave them a way to exit a confrontation, particularly if the U.S. and its allies were willing to offer concessions. Kim Jong Un, Locklear said, appears not to have given himself channels that would help him ratchet down the tensions.
The admiral described Kim Jong Un as "an impetuous young leader (who) continues to focus on provocation rather than on his own people."
The scope of Locklear's responsibilities as the top officer at Pacific Command extend beyond the Korean peninsula, and he told the committee that his command is closely watching the proliferation of submarines among countries including China and Vietnam. Locklear said there are an estimated 300 submarines being operated around the world, although he noted that no country there has an undersea force as capable as the United States'.
Both Russia and China are expected soon to deploy new ballistic missile submarines capable of threatening the United States, Locklear said. India is also expanding its submarine force, and Australia, Singapore, Indonesia, Malaysia, Vietnam, and South Korea have launched, or soon will, modern submarines.