Facing a sudden turbulence triggered by Pyongyang's nuclear test, U.S. President Barack Obama and his administration has been seeking a tougher diplomatic leverage to maintain Northeast Asia's security situation.

The president on Monday had phone talks with his South Korean counterpart Lee Myung-bak and Japanese Prime Minister Taro Aso on the nuclear test by the Democratic People's Republic of Korea (DPRK), in an attempt to coordinate reaction to Pyongyang.

Early on Monday, the DPRK confirmed it "successfully conducted one more underground nuclear test," demonstrating its "self-defensive nuclear deterrent" to the world. Both South Korea and Japan view a nuclear-armed DPRK the major threat to their security.

President Obama and President Lee agreed to "work closely together to seek and support a strong United Nations Security Council resolution with concrete measures to curtail North Korea's nuclear and missile activities," said the White House in a statement.

The president also convinced the Japanese prime minister that the United States has "unequivocal commitment to the defense of Japan and to maintaining peace and security in Northeast Asia," said the White House.

Also in the day, Secretary of State Hillary Rodham Clinton had phone talks with her counterparts from Japan and South Korea to discuss a response to the DPRK's nuclear test, which was the second since 2006.

During talks with Japan's Hirofumi Nakasone and South Korea's Yu Myung-Hwan, Clinton stressed the importance of a "strong, unified approach to this threat to international peace and security," said State Department spokesman Ian Kelly.

"Secretary Clinton is engaged in intensive diplomacy concerning the DPRK's claims of a nuclear test," said Kelly, adding that the top U.S. diplomat will also speak with her Chinese and Russian counterparts late on Monday.

The latest nuclear test by Pyongyang came after the United Nations Security Council adopted a presidential statement in late April, condemning the April 5 rocket launch by the DPRK and demanding the country "not conduct any further launch."

In an official statement on the nuclear test, Obama accused Pyongyang of "recklessly challenging the international community," of violating international law and of constituting "a threat to international peace and security."

The president vowed to hold consultations with its allies and members of the U.N. Security Council on the DPRK's nuclear test and a subsequent series of test-firings of short-range ground-to-air missiles.

The DPRK's nuclear test has triggered global condemnation. The latest blow to Pyongyang comes from the UN Security Council, who condemned the nuclear test as a "clear violation" of existing council resolutions and said it would seek immediately a new resolution.

"The United States thinks this is a grave violation of international law and a threat to regional and international peace and security," said U.S. Ambassador to UN Susan Rice. "Therefore, the United States will seek a strong resolution with strong measures."

(Xinhua News Agency May 26, 2009)