Other senior U.S. military officials echoed those views, saying the U.S. is still trying to gain better intelligence on Kim's intent and his military and technological advancements. North Korea's closed society, they said, has made it difficult to get people into the country and gain access to Kim's inner circle. The officials spoke on condition of anonymity because they were not authorized to speak publicly about the assessment.
Thurman said North Korea's behavior over the past year, including an underground nuclear test, has caused him a great deal of worry. He said the U.S. is working with South Korea to improve its abilities to meet the North's growing asymmetric threats, including the long-range artillery that Pyongyang has arrayed near the border.
He said the U.S. is also working with South Korea to improve its intelligence, surveillance and reconnaissance programs, its cyber security capabilities and its ability to coordinate seamlessly with U.S. forces, including air and maritime.
U.S. control of South Korea's wartime forces is a holdover from the Korean War, and America has been trying for years to build its capabilities. But it has proved difficult to wean the South off its dependence on the U.S. military, particularly as the threat from North Korea has escalated.
Earlier this year, Pyongyang conducted another nuclear test in defiance of United Nations Security Council resolutions. The detonation at a remote underground site was seen as a key step toward the North's goal of building a bomb small enough to fit on a long-range missile capable of striking the U.S.
Last month, a U.S. research institute said recent satellite images appeared to show that North Korea was restarting its plutonium reactor at the Nyongbyon nuclear facility. That facility was closed in 2007 under the terms of a six-nation disarmament agreement.