WASHINGTON — President Obama said in an interview broadcast Tuesday that he did not believe that North Korea yet had the ability to miniaturize a nuclear weapon to fit atop a missile, and he said nothing would shake him from a strategy of refusing to “reward” the kind of provocative behavior exhibited by Kim Jong-un, the North’s leader.

Mr. Obama, speaking in an interview with Savannah Guthrie of NBC News that was recorded just before the bombings in Boston on Monday, implicitly dismissed a conclusion by the Defense Intelligence Agency, which said in a report last month that it had “moderate confidence” that the North already had mastered the technology of building a weapon that could fit into a missile warhead. After the conclusion became public at a Congressional hearing on Thursday, the director of national intelligence, James R. Clapper Jr., issued a statement saying that the agency’s position did not reflect the consensus view of the 15 other intelligence agencies.

Mr. Obama agreed. “You know, based on our current intelligence assessments, we do not think that they have that capacity” to fit a warhead atop a missile, he said. “But, you know, we have to make sure that we are dealing with every contingency out there. And that’s why I’ve repositioned missile defense systems to guard against any miscalculation on their part.”

For the first time, Mr. Obama spoke about Mr. Kim, the North’s young leader, whose motivations have been scrutinized since the latest escalation of threats and tensions began.