North Korea conducted its third nuclear test on Tuesday in defiance of existing U.N. resolutions, angering the United States and Japan and prompting its only major ally, China, to call for calm.

The North said the test had “greater explosive force” than the 2006 and 2009 tests that were widely seen as small-scale. Its KCNA news agency said it had used a “miniaturized” and lighter nuclear device, indicating that it had again used plutonium which is more suitable for use as a missile warhead.

North Korean leader Kim Jong-un, the third of his line to rule the country, has presided over two long-range rocket launches and a nuclear test during his first a year in power, pursuing policies that have propelled his impoverished and malnourished country closer to becoming a nuclear weapons power.

U.S. President Barack Obama labelled the test a “highly provocative act” that hurt regional stability and he and other states that are members of U.N. Security Council pressed for new sanctions on the isolated country.

“The danger posed by North Korea’s threatening activities warrants further swift and credible action by the international community. The United States will also continue to take steps necessary to defend ourselves and our allies,” Obama said in a statement.

The Security Council will meet later on Tuesday to discuss its reaction to the test, although North Korea is already one of the most heavily sanctioned states in the world and has few external economic links that can be targeted.

Japanese Prime Minister Shinzo Abe said the test was a “grave threat” that could not be tolerated. U.N. Secretary-General Ban Ki-moon said the test was a “clear and grave violation” of U.N. Security Council resolutions.

China, which has shown signs of increasing exasperation with its neighbour, repeated calls for the “denuclearisation” of the Korean peninsula and urged its client state and others to react calmly, while pressing Pyongyang not to ramp up tension further, something the North had threatened in the run-up to the test.