The United States says it's committed to defending Japan and opposes any coercive action by China to seize territory under Japanese control in the East China Sea.
Secretary of State John Kerry and his South Korean counterpart say North Korea will gain nothing by threatening tests of its missile or nuclear programs.
Experts say North Korea is probably years away from perfecting the technology to back up its bold threats of a pre-emptive nuclear strike on America, but some aren't sure about nearby targets like South Korea and Japan.
North Korea vowed on Thursday to launch a pre-emptive nuclear strike against the United States, amplifying its threatening rhetoric as U.N. diplomats voted on whether to level new sanctions against Pyongyang for its recent nuclear test.