North Korea test-fired a new, smaller ballistic missile from a submarine, a move that analysts said could be aimed at more quickly fielding an operational missile submarine. Although with a shorter range, a smaller design could mean more missiles stored on a single submarine, potentially putting nuclear-armed North Korea closer to fielding an operational ballistic missile submarine. The White House urged North Korea to refrain from further provocations, with spokeswoman Jen Psaki saying on Tuesday the United States remained open to engaging diplomatically with North Korea over its weapons programs. Pyongyang so far has rejected those overtures. Although both Koreas have been developing increasingly sophisticated weapons, this missile test is expected to have only a limited impact on Pyongyang's arsenal until it makes more progress on a larger submarine that has been seen under construction. Efforts have proven fruitless to bring a negotiated end to the North's nuclear and missile programs in return for U.S. sanctions relief.