WASHINGTON (AP) — Would exploding a hydrogen bomb over the Pacific, as North Korea has threatened, push the current war of words between the U.S. and North Korea closer to actual war?

As with much that has transpired lately in the U.S.-North Korea nuclear crisis, no one can be sure where this would lead or whether the North will even carry out its threat. It does, however, raise many questions, including: How would the North undertake such a nuclear test, what risks might it pose to Japan and how would the U.S. respond?

After the North Korean leader, Kim Jong Un, said President Donald Trump would “pay dearly” for threatening to “totally destroy” North Korea if the U.S. were forced to defend itself or its allies against a North Korean attack, Kim’s foreign minister told reporters his country’s response to Trump “could be the most powerful detonation of an H-bomb in the Pacific.”

All six of North Korea’s nuclear tests thus far, dating to 2006, have been conducted in underground tunnels.

Experts say the most likely way the North would conduct an atmospheric test over the Pacific is to launch a long-range missile — probably overflying Japan — and have its nuclear warhead detonate in the skies over a remote part of the Pacific.