LONDON (BLOOMBERG) - US President Donald Trump revived both his "Rocket Man" nickname for Mr Kim Jong Un and the threat of military force against North Korea, in the latest sign of rising tensions ahead of Pyongyang's year-end deadline.

Mr Trump revisited the name he once used to mock Mr Kim just hours after North Korea said it was preparing a "Christmas gift" for the US if the administration failed to meet its demands by year-end for concessions in nuclear talks.

Mr Kim has repeatedly warned in recent months he could take a "new path" in relations with the US, while resuming ballistic missile launches.

"He definitely likes sending rockets up, doesn't he? That's why I call him 'Rocket Man'," Mr Trump said on Tuesday (Dec 3) during a Nato summit in the UK, adding: "We have the most powerful military we've ever had, and we're by far the most powerful country in the world. And, hopefully, we don't have to use it, but if we do, we'll use it. If we have to, we'll do it."

Despite resuming weapons tests, Mr Kim has refrained from detonating nuclear bombs or launching missiles capable of carrying them to the US while pursuing unprecedented talks with Mr Trump.

North Korea's deadline puts one of Mr Trump's biggest foreign policy achievements on the line just as he gears up for re-election.

Any shift by Mr Kim could come as soon as the North Korean leader's annual New Year's address, which he has previously used to ratchet tensions up and down.

The ruling Workers' Party announced a rare meeting in Pyongyang later this month "to discuss and decide on crucial issues" due to the "changed situation at home and abroad".

Pyongyang's propaganda machine has kicked into high gear in recent months to show Mr Kim as a strong leader.

On Wednesday, the state-run Korean Central News Agency published pictures of him riding a white horse through the snow on Mt Paektu - a sacred site where North Korea says Mr Kim's grandfather and state founder, Mr Kim Il Sung, led guerrillas against the Japanese and his father, Mr Kim Jong Il, was born.

State media praised Mr Kim Jong Un in rhetorical flourishes about the mountain visit - that included his wife, top cadres and military brass - saying he rode a steed "through knee-high virgin snow", connecting himself to "the source of the lifeline of the revolution and inexhaustible patriotism".

While Mr Trump and Mr Kim have held three face-to-face meetings and lavished each other with praise over the past two years, they've achieved little beyond a vague promise to "work toward complete denuclearisation of the Korean Peninsula".

North Korea has continued to expand a nuclear weapons programme that it sees as a vital deterrent against the threat of American invasion.

During their detente, Mr Trump and Mr Kim have held back from the threats and personal insults they flung at each other in 2017 as North Korea conducted a series of weapons tests.

The President notably used the "Rocket Man" moniker in September of that year while threatening to "totally destroy North Korea" during a speech to the United Nations.
North Korea has referred to Mr Trump as a "dotard".

Mr Kim has baulked at US demands for the dismantlement of his weapons programme while Mr Trump has so far rejected North Korea's calls for greater sanctions relief.

The most recent working-level talks between the two sides in October broke down, with North Korea's envoy accusing the American side of arriving "empty-handed".

Mr Trump's current point man for North Korea, Mr Stephen Biegun, will go to Seoul later this month in his first visit to the South Korea capital since the working-level talks with North Korea broke down, the Yonhap News Agency reported, citing an unidentified official at South Korea's foreign ministry.

Although Mr Kim hasn't tested an intercontinental ballistic missile in more than two years, he has reminded the region of his growing military threat with tests of shorter-range missiles, including another volley last week.

North Korea responded to Japanese Prime Minister Shinzo Abe's complaints about the launches with a harshly worded commentary, saying that he "may see what a real ballistic missile is in the not distant future and under his nose".

On Tuesday, Mr Trump also highlighted a key source of friction between the US and its South Korean allies: the President's demands for more military funding.

American negotiators walked out of cost-sharing talks in Seoul last month, after South Korea rejected the administration's demands for as much as a five-fold increase to the approximately US$1 billion (S$1.36 billion) it currently pays.

Mr Trump said those talks had made progress, but it wasn't immediately clear whether he was talking about an agreement for the current year or the period ahead.

"Last year, I asked them to pay more and they agreed," Mr Trump said. "And nobody knows this - I'll say it now, I think, for the first time - but they agreed to pay approximately US$500 million a year or more for protection."