North Korea attempted and failed to launch what experts believe was an intermediate-range ballistic missile on Friday in defiance of U.N. sanctions and in an embarrassing setback for leader Kim Jong Un, drawing criticism from major ally China.
The failed launch, as the reclusive country celebrates the "Day of the Sun" on the birthday of Kim's grandfather, follows the North's fourth nuclear test in January and a long-range rocket launch in February, which led to new U.N. sanctions.
But the North has nevertheless pushed ahead with its missile program, supervised by Kim.
The U.S.-based 38 North website, which specializes in North Korea, has said there has been activity at the country's nuclear site based on satellite imagery, and on Wednesday said the possibility of a fifth nuclear test "could not be ruled out".
China, North Korea's most important economic and diplomatic backer, has been angered by Pyongyang's nuclear tests and rocket launches in the face of U.N. sanctions that China has also backed.