Pyongyang's UN ambassador says its biggest nuclear weapons test yet was a 'gift' addressed to the United States.
North Korea has threatened to send "more gift packages" to the United States, days after testing the biggest nuclear weapon it has ever detonated.
Han Tae-song, ambassador of the Democratic People's Republic of Korea (DPRK) to the United Nations in Geneva, addressed the UN-sponsored Conference on Disarmament on Tuesday after his country carried out its sixth nuclear test.
"I am proud of saying that just two days ago on the 3rd of September, DPRK successfully carried out a hydrogen bomb test for intercontinental ballistic rocket under its plan for building a strategic nuclear force," Han told the Geneva forum.
"The recent self-defence measures by my country, DPRK, are a gift package addressed to none other than the US," Han said.
"The US will receive more gift packages from my country as long as it relies on reckless provocations and futile attempts to put pressure on the DPRK," he added without elaborating.
Military measures being taken by North Korea were "an exercise of restraint and justified self-defence right" to counter "the ever-growing and decade-long US nuclear threat and hostile policy aimed at isolating my country".
"Pressure or sanctions will never work on my country," Han declared. "The DPRK will never under any circumstances put its nuclear deterrence on the negotiating table."
'Threat to us all'
Robert Wood, US disarmament ambassador, said North Korea had defied the international community once again with its test.
"We look forward to working with our partners in the [Security] Council with regard to a new resolution that will put some of the strongest sanctions possible on the DPRK," he told the conference.
"Advances in the regime's nuclear and missile programme are a threat to us all ... Now is the time to say tests, threats and destabilising actions will no longer be tolerated," Wood said.
"It can no longer be business as usual with this regime."
The North Koreans have massive military assets stockpiled on what is the world's most heavily-fortified border with South Korea.
The US has roughly 28,000 troops in South Korea, and there are hundreds of thousands more American citizens just in Seoul, the capital, with a metro area population of 25 million.
Anthony Ruggiero, a sanctions expert at the Foundation for Defense of Democracies, said the next logical step is for the US to impose "secondary sanctions" targeting banks or businesses in China that do business with North Korea - a tactic the US used effectively to push Iran to the table over its nuclear programme several years ago.
"The chance for sanctions to work is that playbook," Ruggiero said.
But Russian President Vladimir Putin said imposing tougher sanctions on North Korea over its nuclear missile programme would be counterproductive, warning that threats of military action could trigger "a global catastrophe".
"Russia condemns North Korea's exercises; we consider that they are a provocation ... [But] ramping up military hysteria will lead to nothing good. It could lead to a global catastrophe," Putin said on Tuesday after a BRICS summit in Xiamen, China.
"There's no other path apart from a peaceful one."
China, backed by Russia, has been urging an immediate return to talks, predicated on the US halting joint military exercises with South Korea and North Korea suspending its weapons development.
But few in the US government have advocated direct talks with the North Koreans until their behaviour significantly changes.