South Korea , South Korea 's and South Korea 's warn of `` significant consequences '' after a bomb test . Lee paid a visit to the underground bunker that serves as the South 's crisis management center , his press office reported . U.S. officials say a new Stalinist nuclear test could come at any time . U.S. president tells his government to be prepared .
South Korea , South Korea 's and South Korea 's warn of `` significant consequences '' after a bomb test . U.S. officials say a new Stalinist nuclear test could come at any time . U.S. president tells his government to be prepared .