North Korea is once again threatening the United States and South Korea -- this time over joint naval drills taking place in the Yellow Sea.
The drills come ahead of a joint summit in Washington by the leaders of the two allies.
North Korea says it will hit back if any of the shells fall on its side of the disputed maritime border during scheduled South Korean-U.S. military drills. If the allies respond, Pyongyang vows to strike five South Korean islands.
"It's premature to make a judgment about whether the North Korean provocation cycle is going up, down or zigzagging," said Danny Russel, senior director for East Asia on Obama's National Security Council.
"Many analysts have anticipated that the North Korean provocation cycle would culminate in some sort of a grand fireworks display, and no one can rule that out," Russel said.