UPDATE (Tuesday, 6:30 a.m.) The Associated Press is reporting that North Korea confirmed it has successfully conducted its third underground nuclear test.
North Korean officials say the test was its "first response" to U.S. threats and the country will continue with "second and third measures of greater intensity" if the U.S. continues to be hostile toward the nation.
The North Korean Foreign Ministry released a statement saying the nuclear test was a self-defensive measure and does not violate any international law.
SEOUL, South Korea (AP) -- The U.S. Geological Survey has detected a magnitude 4.9 earthquake in North Korea.
It isn't immediately clear whether North Korea has conducted its widely anticipated third nuclear test.
The U.S. agency made the announcement on its website Tuesday.
South Korean government officials couldn't immediately determine whether a nuclear blast or natural earthquake had taken place in the North.