North Korea confirmed on Wednesday it test-fired a new, smaller ballistic missile from a submarine.
A day earlier South Korea's military said a missile was fired off the east coast near Japan, from the port of Sinpo in North Korea, where they keep its submarines.
North Korean state media KCNA released photos that appeared to show a thinner, smaller missile than earlier submarine-launched ballistic missile designs.
A smaller missile could advance more quickly on a submarine, analysts say.
It may also be a previously unseen model showcased at an exhibition in Pyongyang last week.
The smaller design mean more could be stored in a single submarine, although fired with a shorter range.
It is the latest in a string of North Korean missile tests, and comes as South Korea also develop its own weapons and tests in recent weeks.
The White House urged North Korea to refrain from further "provocations."
Spokeswoman Jen Psaki said the U.S remained open to talks over North Korea's weapons programs.
But Pyongyang has so far rejected those offers.
North Korean leader Kim Jong Un was not reported to have attended Tuesday's test.