North Korea test-fired what appeared to be two intermediate range ballistic missiles on Thursday, but both failed, the U.S. military said, in a setback for North Korean leader Kim Jong Un ahead of next week's ruling party congress.
The isolated nation has conducted a series of missile launches in violation of U.N. resolutions ahead of the Workers' Party congress which begins on May 6.
South Korea also says North is ready to conduct a new nuclear test at any time.
China said the U.N. Security Council was working on a response to North Korea's latest missile tests, while U.N. Secretary-General Ban Ki-moon urged Pyongyang to cease "further provocative actions."
Thursday's tests looked to have been hurried, according to a defense expert in Seoul, and follow a failed launch of a similar missile earlier this month.