What was initially considered a 4.9 magnitude earthquake in North Korea turned out to be a nuclear bomb test in defiance of United Nations resolutions.

The North Korean government confirmed the test about three hours after the U.S. Geological Survey reported a “shallow, 4.9 magnitude earthquake near a nuclear facility.” What was initially feared to be a potential nuclear accident has turned into a completely different fear.

The United Nations Security Council immediately scheduled an “emergency meeting” for Tuesday morning in New York. UN Secretary General Ban Ki-moon called the test a “clear and grave violation” of UN resolutions.

The state-run KCNA news service reported the test was a “miniaturized and lighter nuclear device” and that it “did not pose any negative impact on the surrounding ecological environment.”

North Korea previous conducted nuclear tests in 2006 and 2009.