WASHINGTON — The White House reacted to North Korean claims of a hydrogen bomb detonation Wednesday by casting doubt, while Republicans in Congress urged a tough response.

White House Press Secretary Josh Earnest said the initial analysis was "not consistent" with the regime's claims, but called the nuclear test a "provocative and a flagrant violation of United Nations Security Council resolutions."

Based on reports of the test, the Security Council will consider sanctions against Pyongyang, Earnest said.

The US intelligence community is expected to provide the White House with "a more robust assessment," Earnest said.

US National Security Adviser Susan Rice discussed the matter in person with Chinese Ambassador Cui Tiankai on Wednesday, in line with the White House's expectation that China play a significant role on the issue.

Earnest expressed the US commitment to protecting the national security of its allies in South Korea, where the US maintains a significant military presence.

Among other US officials in touch with their counterparts in the region following the alleged test, Secretary of State John Kerry communicated with his South Korean counterpart, as did Defense Secretary Ash Carter with his South Korean counterpart.

Carter and South Korean Minister of National Defense Han Min-koo spoke by phone to discuss potential alliance responses to the recent apparent North Korean nuclear test, according to a Pentagon statement. Both agreed such a test "would be an unacceptable and irresponsible provocation and is both a flagrant violation of international law and a threat to the peace and stability of the Korean pPeninsula and the entire Asia-Pacific region," it reads.

In a statement shortly after the DPRK announcement, State Department spokesman John Kirby said the US is "monitoring and continuing to assess the situation in close coordination with our regional partners" and called on North Korea to abide by international standards.

"North Korea conducted its first nuclear test in 2006 and, until today, has done so twice since, but we have consistently made clear that we will not accept it as a nuclear state," Kirby said. "We will continue to protect and defend our allies in the region, including the Republic of Korea, and will respond appropriately to any and all North Korean provocations."

State Department Spokesman John Kirby speaks during a Jan. 6 briefing at the State Department in Washington.

Photo Credit: Mandel Ngan/AFP

The three previous tests in 2006, 2009 and 2013 triggered waves of UN sanctions. The new test, which came just two days before North Korean leader Kim Jong-un's birthday, was initially detected as a 5.1-magnitude tremor at the North's main Punggye-ri nuclear test site in the northeast of the country.

Most experts had assumed Pyongyang was years from developing a hydrogen bomb, while assessments were divided on how far it had gone in developing a miniaturized warhead to fit on a ballistic missile.

Whatever the nature of the device, it marked a striking act of defiance in the face of warnings from enemies and allies alike that Pyongyang would pay a steep price for moving forward with its nuclear weapons program.

It throws down a particular challenge to US President Barack Obama, who, during a visit to South Korea in 2014, vowed sanctions with "more bite" if Pyongyang went ahead with another test.

The chairman of the US House Armed Services Committee, Rep. Mac Thornberry R-Texas, released a statement calling for the deployment of missile defense systems in South Korea and to strengthen its homeland defenses.

"The US must work with our South Korean allies to deploy missile defense systems, including THAAD, on the peninsula and work at home to strengthen our homeland defenses," Thornberry said, using an acronym for the Theater High Altitude Area Defense, an anti-ballistic missile system.

"We must also take immediate steps to strengthen our own nuclear deterrent, which is the foundation for our other defense capabilities," he said.

Thornberry, and other Republicans, took the occasion to frame the test as a failure of the administration's foreign policy.

The International Campaign to Abolish Nuclear Weapons also issued a statement warning that North Korea's action "fuels the misguided and dangerous notion that the threat of nuclear weapons is an effective deterrent."

"The new test by the DPRK is another indication of the inability of the current nuclear regime to prevent states from seeking, possessing or modernizing nuclear weapons," the ICAN statement reads. "The absence of a clear norm that prohibits nuclear weapons has persuaded some states that their possession and the threat of their use are somehow still legitimate. This could lead to a new arms race more dangerous than the one we faced during the Cold War."

Those comments echo those made by former US Secretary of Defense William Perry in December, when he warned the US is on the "brink" of a new nuclear arms race.

"I see an imperative," Perry said then, "to stop this damn nuclear arms race from accelerating again."

With additional reporting by Agence France-Presse.

Aaron Mehta was deputy editor and senior Pentagon correspondent for Defense News, covering policy, strategy and acquisition at the highest levels of the Defense Department and its international partners.

Joe Gould was the senior Pentagon reporter for Defense News, covering the intersection of national security policy, politics and the defense industry. He had previously served as Congress reporter.

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