The United States is ready to use its nuclear weapons against North Korea if the country continues to threaten Washington or its allies, the White House has warned, amid escalating tensions between the two countries.

US President Donald Trump held a conversation with Japanese Prime Minister Shinzo Abe on Sunday, after North Korea conducted a test of a hydrogen bomb.

The White House published a readout of Trump�s talks with Abe that said the US is ready to use the “full range” of capabilities at its disposal in dealing with North Korea.

"President Trump reaffirmed the commitment of the United States to defending our homeland, territories, and allies using the full range of diplomatic, conventional, and nuclear capabilities at our disposal," the readout said.

North Korea on Sunday announced it had conducted a “successful” hydrogen bomb test, hours after two tremors were detected in the country.

“The hydrogen bomb test was a perfect success,” North Korean state television said, adding that the device was capable of being loaded onto long-range missiles.

The North Korean broadcaster said the nuclear test had an “unprecedentedly large power,” and that it “marked a very significant occasion in attaining the final goal of completing the state nuclear force.”

Trump and the Japanese PM both condemned North Korea’s nuclear test and called the country’s behavior “destabilizing and provocative actions,” the statement read.

Trump also “confirmed the two countries� ironclad mutual defense commitments, and pledged to continue close cooperation,” it stated.

The Trump administration’s mentioning of "nuclear capabilities" was the strongest reaction given on Sunday.

Earlier, the Pentagon chief James Mattis warned of a “massive military response” to any North Korean threats, but he stopped short of threatening the country with a nuclear attack.  

"Any threat to the United States or its territories including Guam or our allies will be met with a massive military response," Mattis said.

Last week, North Korea’s leader Kim Jong-un ordered the production of more rocket warheads and engines, shortly after the United States suggested that its threats of military action and sanctions were having an impact on Pyongyang’s behavior.

Pyongyang says it will not give up on its nuclear deterrence unless Washington ends its hostile policy toward the country and dissolves the US-led UN command in South Korea. Thousands of US soldiers are stationed in South Korea and Japan.