(RFE/RL) -- North Korea is facing international criticism after announcing it has carried out what it calls a "successful" underground nuclear test.
North Korea "successfully conducted one more underground nuclear test on May 25 as part of its measures to bolster its nuclear deterrent for self-defense in every way as requested by its scientists and technicians," state television announced.
Officials in North Korea say the underground nuclear test helped resolve scientific and technological problems so that they can increase their nuclear-weapons capabilities in terms of "explosive power and technology of its control."
Adding to international concerns are unconfirmed media reports that the North also carried out a series of short-range missile tests on May 25.
Even before the nuclear test was independently confirmed, Japan's Chief Cabinet Secretary Takeo Kawamura told reporters in Tokyo that the move was a serious violation of a deal made with North Korea during six-party nonproliferation talks.
"If North Korea did indeed conduct a nuclear test, this would be a clear violation of the UN Security Council resolution and we cannot ever allow this," Kawamura said.
He added that "we will be coordinating with the concerned nations including the United Nation's Security Council to take resolved action."
In Beirut, Russian Foreign Minister Sergei Lavrov also expressed concern before the test had been independently confirmed
Russia's Defense Ministry later confirmed that North Korea had conducted an underground nuclear device with the explosive strength of between 10 and 20 kilotons -- comparable to power of the atomic bombs dropped on Hiroshima and Nagasaki. It said the detonation was registered about 80 kilometers northwest of the city of Kilchu.
The separate short-range missile tests -- reported by South Korea's Yonhap news agency -- were not immediately confirmed.
Russia, current chair of the Security Council, has convened an emergency meeting of the 15-member body for 2000 GMT to discuss the issue. Both Japan and South Korea have formed crisis-management teams.
The United States, Japan, Russia, and South Korea -- along with China -- have been involved in the six-party talks with North Korea since 2003.
Those talks were aimed at putting an end to North Korea's nuclear programs. In October 2006, the North carried out its first nuclear-weapons test. In 2007, the forum reached a landmark deal under which Pyongyang was to receive energy aid and security guarantees in exchange for disarming.
But North Korea withdrew from those negotiations last month after firing a long-range rocket in what it had called a satellite launch. Many countries saw that April launch as a disguised ballistic-missile test. The UN Security Council condemned the launch and, in response, tightened sanctions on North Korea.
North Korea had been threatening to carry out this latest nuclear test in response to those tighter international sanctions.
In Washington, U.S. President Barack Obama has called for a global response to the North Korean tests, which he called a "threat to international peace."
The European Union, Britain, and France also have added their voices to the chorus of international concern.
British Prime Minister Gordon Brown called North Korea's nuclear test a "danger to the world" that will undermine peace prospects on the Korean Peninsula. Brown also described the test as "erroneous" and "misguided," saying it will do nothing for North Korea's security.
Brown also said that the North Korea can only expect renewed isolation from the international community if it does not behave responsibly.
A statement from India's Foreign Ministry said it was "unfortunate" that North Korea conducted a nuclear test "in violation of its international commitments."
India says that it is concerned, like others in the international community, about the adverse effect that such tests have on peace and stability in the region.
A senior official at the North Korean Embassy in Moscow rejected the international criticism today, telling the ITAR-TASS news agency that more nuclear tests are possible "if the United States and its allies continue their policy of intimidation" toward North Korea.
North Korea also says it will no longer attend six-party talks on its nuclear program.
U.S. House of Representatives Speaker Nancy Pelosi, in China on an official visit, said in a statement that she would bring a message to the Chinese leadership asking them to use "their influence to help bring North Korea back to the table for the six-party talks."