WASHINGTON — North Korea’s confirmation Tuesday that it had conducted its third, long-threatened nuclear test provoked international rebukes and elicited pledges of more punitive action from UN Security Council members.
The official KCNA news service of North Korea said the country had used a ‘‘miniaturized and lighter nuclear device with greater explosive force than previously’’ and that the test ‘‘did not pose any negative impact on the surrounding ecological environment.’’
Early Tuesday, the office of the director of national intelligence, James R. Clapper Jr., issued a statement suggesting the North Koreans were, on their third try, beginning to produce nuclear devices with substantial explosive power.
“The explosion yield was approximately several kilotons,’’ the announcement said, which was less specific than a South Korean Defense Ministry estimate of six to seven kilotons.
That would be far greater than the yield of less than one kiloton detected in the North’s 2006 test, but it is unclear how it would measure up to the last test, in 2009, which had an estimated yield of two to six kilotons. By comparison, the first bomb the United States dropped on Japan, which devastated Hiroshima in 1945, had a yield of 15 kilotons.
The claim about miniaturizing the device could be important, if true. But there has been no proof yet that the North has mastered the difficult technology of making bombs small enough to be fitted to ballistic missiles that eventually could reach the US mainland.
The test drew a crescendo of denunciations, with President Obama calling it a ‘‘highly provocative act’’ that demands ‘‘swift and credible action by the international community’’ against North Korea. Russia, Britain, South Korea, and the United Nations also condemned the blast. The head of the international nuclear watchdog called the test ‘‘deeply regrettable,’’ and the Security Council, which has passed three resolutions aimed at punishing North Korea for its nuclear weapons-related work, met in emergency session to devise a fourth resolution.
Foreign Minister Kim Sung-Hwan of South Korea, whose country holds the monthly rotating presidency of the Security Council, emerged from the meeting before noon to read a statement from all 15 members that they had ‘‘strongly condemned this test’’ and were beginning to work immediately on a resolution. He declined to specify what was envisioned but emphasized that all members, including North Korea’s ally and neighbor China, wanted action that would persuade the North to abandon its nuclear ambitions.
The South Korean foreign minister also said North Korea would ‘‘be held responsible for any consequences of this provocative act.’’
Susan E. Rice, the US ambassador to the United Nations, told reporters that the Security Council ‘‘must and will deliver a swift, credible, and strong response.’’ She also declined to specify what a new resolution might do. “We and others have a number of further measures that we will be discussing,’’ she said.
The test is the first under the country’s new leader, Kim Jong Un, and an open act of defiance to the Chinese, who had urged Kim not to risk open confrontation by setting off the weapon. In a relatively muted statement issued several hours after the blast, China expressed its ‘‘staunch opposition’’ to the test but called for ‘‘all parties concerned to respond calmly.’’
Later Tuesday, the North Korean Foreign Ministry warned of ‘‘second and third measures of greater intensity’’ if Washington remains hostile.
It may take days or weeks to determine independently whether the test was successful. US officials will also be looking for signs of whether the North, for the first time, conducted a test of a uranium weapon, based on a uranium enrichment capability it has been pursuing for a decade.
The KCNA news agency said the test demonstrated that the country’s nuclear deterrence has become ‘‘diversified.’’ South Korean officials said they were studying whether it meant North Korea had used highly enriched uranium for bomb fuel, rather than plutonium.