Updated 3:50 p.m. ET
PYONGYANG, North Korea North Korea said the atomic test it conducted Tuesday in the remote, snowy northeast was merely its "first response" taken with "maximum restraint," in response to what it called U.S. threats, and said it will continue with unspecified "second and third measures of greater intensity" if Washington maintains its hostility.
The underground test, which set off powerful seismic waves, was a crucial step toward its goal of building a bomb small enough to be fitted on a missile capable of striking the United States. The test drew immediate condemnation from Washington, the U.N. and others. Even its only major ally, China, voiced opposition.
After the launch was first reported, U.S. officials confirmed that there are indications that North Korea intends to conduct a second test of its arsenal, reports CBS News correspondent Margaret Brennan.
A source familiar with the regional threat assessment says that North Korea has been considering doing "two for the price of one," in other words, conduct two tests in anticipation of punishing U.N. action.
CBS News correspondent David Martin reports that the second test could be a missile, according to intelligence assessments made in recent days.
North Korea has been warning of the nuclear test for weeks, but U.S. officials consider the timing of the test to be especially provocative as it comes during the Chinese New Year holiday week, ahead of China's political transition, and on the cusp of the U.S. State of the Union address.
President Barack Obama said nuclear tests "do not make North Korea more secure." Instead, North Korea has "increasingly isolated and impoverished its people through its ill-advised pursuit of weapons of mass destruction," he said in a statement.
North Korea claimed the device was smaller than in previous tests; Seoul said it likely produced a bigger explosion.
The Office of the Director of National Intelligence confirmed the test Tuesday, saying in a statement: "The U.S. Intelligence Community assesses that North Korea probably conducted an underground nuclear explosion in the vicinity of P'unggye on February 12, 2013. The explosion yield was approximately several kilotons. Analysis of the event continues."
The test was a defiant response to U.N. orders to shut down atomic activity or face more sanctions and international isolation. It will likely draw more sanctions from the United States and other countries at a time when North Korea is trying to rebuild its moribund economy and expand its engagement with the outside world.
The Security Council met Tuesday, and all 15 members agreed the "" from North Korea warranted a harsh response.
CBS News foreign affairs analyst Pamela Falk reports that China's backing of new sanctions after the North's December rocket launch is a strong indication that the Security Council will be able to pass a tough new resolution. There is new leadership in China, South Korea, North Korea and Japan and there is an increasing concern in the international community that Pyongyang's nuclear test could destabilize the region.
Several U.N. resolutions bar North Korea from conducting nuclear or missile tests because the U.N. Security Council considers Pyongyang a would-be proliferator of weapons of mass destruction and its nuclear testing a threat to international peace and stability. North Korea dismisses that as a double standard, and claims the right to build nuclear weapons as a defense against the United States, which has been seen as enemy No. 1 since the 1950-53 Korean War. The U.S. stations more than 28,000 troops in South Korea to protect its ally.
North Korea appears defiant in the face of further sanctions, telling the U.N. disarmament forum on Tuesday that it would never bow to resolutions on its nuclear program and that prospects were "gloomy" for the denuclearisation of the divided Korean peninsula because of a "hostile" U.S. policy, Reuters reports.
"The U.S. and their followers are sadly mistaken if they miscalculate the DPRK would respect the entirely unreasonable resolutions against it. The DPRK will never bow to any resolutions," Jon Yong Ryong, first secretary of North Korea's mission in Geneva, told the Conference on Disarmament, referring to the Democratic People's Republic of Korea (DPRK).
He said: "If the EU (European Union) truly wants peace and security on the Korean peninsula, it should urge the U.S. first to terminate its hostile policy towards DPRK on an impartial basis."
Tuesday's test is North Korea's first since young leader Kim Jong Un took power of a country long estranged from the West. The test will likely be portrayed in North Korea as a strong move to defend the nation against foreign aggression, particularly from the U.S.
"The test was conducted in a safe and perfect way on a high level, with the use of a smaller and light A-bomb, unlike the previous ones, yet with great explosive power," North Korea's official Korean Central News Agency said, confirming speculation that seismic activity near Kilju around midday was a nuclear test.
North Korea was punished by more U.N. sanctions after a December launch of a rocket that the U.N. and Washington called a cover for a banned missile test. Pyongyang said it was a peaceful, and successful, bid to send a satellite into space.
The timing of the test is significant. It came hours before Mr. Obama's speech and only days before the Saturday birthday of Kim Jong Un's father, late leader Kim Jong Il, whose memory North Korean propaganda has repeatedly linked to the country's nuclear ambitions.
This year also marks the 60th anniversary of the signing of the armistice that ended the 1950-53 Korean War, and in late February South Korean President-elect Park Geun-hye will be inaugurated.
In Pyongyang, where it was snowing Tuesday, North Koreans gathered around televisions to watch a 3 p.m. TV broadcast announcing the nuclear test.
The test shows the world that North Korea is a "nuclear weapons state that no one can irritate," Kim Mun Chol, a 42-year-old Pyongyang citizen, told The Associated Press in the North Korean capital. "Now we have nothing to be afraid of in the world."
The National Intelligence Service in Seoul told lawmakers that North Korea may conduct an additional nuclear test and test-launch a ballistic missile in response to U.N. talks about imposing more sanctions, according to the office of South Korean lawmaker Jung Chung-rae, who attended the private meeting. Analysts have also previously speculated that Pyongyang might conduct multiple tests, possibly of plutonium and uranium devices.
North Korea is estimated to have enough weaponized plutonium for four to eight bombs, according to American nuclear scientist Siegfried Hecker.