Maria Zakharova, a spokeswoman for the foreign ministry, said that a search that U.S authorities carried out at Russia's diplomatic facilities was an attempt to prove that Moscow meddled in USA presidential elections, TASS state news agency reported. Last week, after Trump said that "talking is not the answer", Defense Secretary James Mattis followed up by saying: "We're never out of diplomatic solutions".
"They only understand one thing!"
"The National security team is monitoring this closely", Sanders said. It was the first nuclear test since Trump took office in January.
The U.S. Geological Survey said it recorded a 6.3 magnitude quake in North Korea on Sunday.
But there were several signs that Pyongyang's claims stood to at least some scrutiny, leading experts to believe that if the country had not developed a hydrogen bomb yet it was getting awfully close.
The bomb was created to be mounted on its newly developed intercontinental ballistic missile (ICBM), North Korea said.
That kind of power makes it hard to think it's anything but a hydrogen bomb test.
The test represents a significant escalation in the conflict between North Korea and the US, and another act of defiance in response to President Trump's bluster toward the regime.
North Korea's sixth nuclear test was expected.
"This new test, which follows the two tests previous year and is the sixth since 2006, is in complete disregard of the repeated demands of the worldwide community", he added. This morning's nuclear test coincides with our Labor Day weekend, and the anniversary of the North Korean government's founding.
"Their words and actions continue to be very hostile and risky to the United States", Trump said in the first of a series of tweets.
He branded North Korea "a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success".
Mrs May blasted North Korea "reckless" and called for further pressure to be placed on Pyongyang to force the state to give up its quest for ICBMs.
North Korean leader Kim Jong Un.
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Russian Federation called for dialogue and negotiations to deal with the North Korean threat.
South Korea's new president, Moon Jae-in, has argued for continuing dialogue with its neighbor over its nuclear program, while also supporting global sanctions.
Trump and Japanese prime minister Shinzo Abe discussed the growing threat from the North Korean actions on Sunday.
Nuclear tests are crucial to perfecting sophisticated technologies and to demonstrating to the world that claims of nuclear prowess are not merely a bluff.
Veteran North Korea state news anchor Ri Chun Hee hailed the test as a "perfect success" and the final step in attaining a "state nuclear force".
There was no immediate independent confirmation of the North's claim.
Now, with his nation's most powerful nuclear detonation Sunday, and a string of missile launches, including one over Japan, Kim has effectively called the President's bluff, escalating a risky foreign policy crisis.
At the same time, the simple power of the blast was convincing. It allows the weapons to pack a huge punch while fitting in a warhead small enough to be delivered by a missile.
"We can not deny it was an H-bomb test", Onodera said. North Korea had made an absurd tactical mistake by committing a series of provocations such as launching ICBM [long-range] missiles and conducting a nuclear test, which was heightened tensions on the [Korean] peninsula and is threatening world peace. It has defied United Nations sanctions and worldwide pressure to develop nuclear weapons and to test missiles which could potentially reach the mainland US.
Pyongyang could launch another ICBM in the next few months, Cha said.
And the North has thousands of conventional artillery pieces within range of the South Korean capital Seoul. "I don't have any serious doubt in my mind that this is what the North Koreans say it is, and that's a thermonuclear weapon".
"In comparison, the explosive yield of the nuclear bomb dropped on Hiroshima on 6 August 1945 was estimated at 15 kilotons TNT, while the bomb dropped on Nagasaki three days later was 20 kilotons TNT", NORSAR said in a statement.
Instead, she is working on training the next generation of North Korea's newsreaders. Kim signed off on the plan, but is watching the moves by the US before deciding when or whether to carry it out.
But Mr Johnson urged Beijing to go further in putting economic pressure on its neighbour. About 28,500 American troops are deployed in South Korea as deterrence against North Korea.