North Korea has made considerable progress this year on weapons technology, including testing a submarine-launched missile for the first time, but it is still not clear if the isolated nation has developed a nuclear warhead.

It also does not yet have a fleet of submarines that can launch the newly developed missile.

Nevertheless, concerns about the threat posed by North Korea have spiraled since it conducted its fourth nuclear explosion in January and followed it up with a series of missile tests despite severe United Nations sanctions.