Clapper's warning came Tuesday at a hearing on security threats to the United States by the Senate Select Committee on Intelligence, headed by Sen. Dianne Feinstein, D-Calif.
When asked by Feinstein whether North Korea, in light of its various threats, including the scrapping of the 1953 Korea Armistice this week, could renew hostilities with South Korea, Clapper said:
"Absolutely. I personally, having followed Korea ever since I served there in the mid '80s as the director of intelligence for U.S. Forces Korea, am very concerned about the actions of the new young leader and very belligerent, and the rhetoric that has been emanating from the North Korean regime."
Clapper was referring to Kim Jong Un, the new leader of the isolated, impoverished Communist country who took over in December of 2011 after the death of his father. North Korea has stepped up its highly provocative and dangerous threats since the U.N. Security Council severely tightened existing sanctions in response to the North's Feb. 12 nuclear test and its earlier long-range missile test.
"The rhetoric, while it is propaganda-laced, is also an indicator of their attitude and perhaps their intent," Clapper said. "So for my part, I am very concerned about what they might do. And they are certainly, if they chose -- so chose -- could initiate a provocative action against the South."
John Brennan, the new director of the U.S. Central Intelligence Agency who also spoke to the Senate committee, agreed with Clapper's assessment about North Korea.
"This is a very dynamic time right now with the new leader. I think it also just underscores the importance of making sure that our analytic capabilities, as well as our collection capabilities, are as strong as possible. Because, what we're talking about are developments that have strategic importance and potential consequence for U.S. interests, not just in northeast Asia, but also globally."
Brennan said the region is one of the areas that "we as the intelligence community, and certainly the CIA, need to pay particularly close attention to."
In his written testimony to the Senate committee, Clapper said the North Korean military "is well postured to conduct limited attacks with little or no warning" against South Korea, Kyodo News reported.