America must take “literally” the threat of North Korea conducting a powerful nuclear test over the Pacific Ocean, according to a top official.

Dramatically upping the stakes as it showcases its bolstered military prowess, North Korea last month conducted its first test of a powerful hydrogen bomb. Shortly afterward, the country’s foreign minister responded to Donald Trump’s threat to “totally destroy” North Korea by saying the country could conduct the “strongest hydrogen bomb test over the Pacific Ocean”.

It was not an idle warning, according to senior diplomat Ri Yong Pil, who told CNN the possibility was meant to be taken “literally”.

“The foreign minister is very well aware of the intentions of our supreme leader, so I think you should take his words literally,” Mr Ri told CNN.

The threat of a nuclear test came as North Korea renewed its warning that America was provoking a military conflict, calling joint naval exercises a prelude to “nuclear war”.

The claim, made in a letter from North Korean ambassador Ja Song Nam, is the latest in a series of threats and recriminations America and North Korea have exchanged over a tense few months. As North Korea has tested increasingly powerful weaponry and threatened to obliterate its enemies, the Trump administration has responded with vows to punish Korea with force if necessary.

Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Show all 6 1 /6 Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Photos released by North Korea show Kim Jong-un talking to subordinates next to a device thought to be the new thermonuclear weapon. There is no way of independently verifying the pictures STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb North Korea claims it has successfully tested an advanced hydrogen bomb which could be loaded onto an intercontinental ballistic missile AFP/Getty Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A diagram on the wall behind Mr Kim shows a bomb mounted inside a cone STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb North Korean leader Kim Jong-Un (C) attending a photo session with participants of the fourth conference of active secretaries of primary organisations of the youth league of the Korean People's Army (KPA) in Pyongyang STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A new stamp issued in commemoration of the successful second test launch of the "Hwasong-14" intercontinental ballistic missile KCNA via Reuters Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A new stamp issued in commemoration of the successful second test launch of the "Hwasong-14" intercontinental ballistic missile KCNA via Reuters

It has also conducted joint military exercises with South Korea, including a Navy drills that dispatched around 40 vessels -among them the nuclear-powered USS Ronald Reagan aircraft carrier - near the Korean Peninsula this month.

At the time North Korea referred to those drills as a “rehearsal for war”. In his letter, Mr Ja asked the United Nations Security Council to examine what he called the “general mobilization of the strategic assets” for the exercise.

CIA Chief Mike Pompeo says threat of North Korea

Mr Ja said Donald Trump “made the most ferocious declaration of war in history by claiming to ‘totally destroy’” North Korea. The President issued that warning during a mid-September speech to the United Nations, continuing to match Korean bellicosity with American warnings of military reprisal. Defense Secretary James Mattis had said weeks earlier that North Korea risked “total annihilation” if it continued to defy the world and threaten allies.

The latest provocations from North Korea come as Mr Trump makes final preparations for a trip across Asia at the start of next month, that will include stops in Japan, South Korea and China. On Wednesday he tweeted that he had spoken with China's President Xi Jinping about the issue of North Korea.

Mr Trump also said he congratulated Mr Xi for his "extraordinary elevation" after China's president consolidated his grip on power in the country with a new leadership line-up unveiled at the Communist Party Congress in Beijing.

Mr Xi told Trump China would “unswervingly follow the path of peaceful development” and promote “coordination and cooperation among world major powers”, the state Xinhua news agency reported.

“China attaches great importance to the Sino-US relations and is willing to promote the long-term, healthy and stable development of bilateral relations on the basis of mutual respect and mutual benefits,” Xinhua cited Mr Xi as saying.

Mr Trump was also earlier asked by reporters whether he would visit the tense demilitarized zone dividing North and South Korea during his Asia tour - his response was typically cryptic.

“I'd rather not say, but you'll be surprised,” he said.

China, seen as crucial to reining in its belligerent neighbor, has joined the world effort to halt North Korea but has also echoed the country’s warnings about US military exercises functioning as acts of aggression.

In August, the country’s foreign ministry urged America to suspend planned military drills that it warned would escalate tensions. A state editorial condemning North Korea’s nuclear test in September also reprimanded the US for its “belligerent tone”, cautioning that “military exercises on DPRK's doorstep ate into Pyongyang's sense of security” and suggesting that North Korea suspend its military programs in exchange for the suspension of military exercises.

North Korean leader Kim Jong-un also sent a rare congratulatory message to Mr Xi, the North's state media said on Thursday, wishing the Chinese leader “great success” in his future tasks as head of the nation.

It was a warm overture from the North Korean leader, who rarely issues personal messages. “It expressed the conviction that the relations between the two parties and the two countries would develop in the interests of the peoples of the two countries,” the North's state-run central news agency said in a statement.

The UN Security Council to which Mr Ja issued his plea has had limited success in containing North Korea. It has clamped successive rounds of sanctions on the North Korean economy but failed to deter the nation's military ambitions, leading American ambassador to the the UN Nikki Haley to declare diplomatic options “exhausted”.

A leading South Korea opposition figure, Hong Jun-pyo, head of the conservative Liberty Korea Party, told Reuters in Washington that he backed Mr Trump's tough stance.