(CNN) A senior member of the North Korean government has again described Donald Trump as a "dotard" after the US President revived the war words with North Korean leader Kim Jong Un by calling him "Rocket Man."

Choe Son Hui, North Korea's First Vice-Foreign Minister, was quoted by North Korea's state news agency as saying the foreign ministry "can not repress displeasure over the utterances made by President Trump inappropriately at the most sensitive time."

Choe added: "If any language and expressions stoking the atmosphere of confrontation are used once again on purpose at a crucial moment as now, that must really be diagnosed as the relapse of the dotage of a dotard."

Speaking of the North Korean leader at the NATO summit in London on Tuesday, Trump said: "He really likes sending rockets up, doesn't he? That's why I call him Rocket Man." Trump added that he and Kim have "a good relationship."

The statement on Thursday is the latest in a series of increasingly dire warnings by North Korea, and recalls the strong language between the two leaders that escalated in 2017, before a landmark meeting the following year in Singapore.

Pak Jong Chon, the chief of staff of the Korean People's Army, said Wednesday that Kim was "displeased" by what he called "undesirable remarks" about North Korea made by US President Donald Trump on Tuesday in London, where he was attending NATO meetings.

Pak's comments come amid a ratcheting up in rhetoric from the North Koreans ahead of the country's self-imposed end-of-year deadline for negotiations with the US.

A foreign ministry official said earlier this week that Pyongyang was preparing a "Christmas gift," for Washington, but warned that the present the Trump administration will receive depends on events in the coming days.

When Trump was asked about North Korea's recent uptick in missile tests and the status of nuclear talks Tuesday, he referred to Kim as "Rocket Man" -- a nickname the President coined during the standoff between Pyongyang and Washington in 2017 -- and hinted that his administration reserved the right to use force.

This undated photo released by North Korea's official Korean Central News Agency Wednesday shows North Korean leader Kim Jong Un (center), his wife Ri Sol Ju (right, in black) and Pak Jong Chon (left, in the grey hat) visiting Mount Paketu.

"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," Trump said.

Those comments appear to have rubbed Kim and the top North Korean leadership the wrong way.

High-ranking North Korean army officials like Pak do not often issue public statements, and when they do they're usually focused on tensions between North and South Korea, according to Michael Madden, an expert in North Korean leadership at the Stimson Foundation.

Pak was recently photographed alongside Kim on horseback touring Mount Paektu, an important site in North Korean lore, often used for propaganda purposes. That means it's likely his statement Wednesday carries added weight.

Pak said that while he recognized Trump attached preconditions when discussing the use of military force against North Korea, the President's comments still "greatly disappointed" him.

"Such elated spirit and bluffing may greatly get on the nerve of the dialogue partner even at the slightest slip," he said. "The use of armed forces against the DPRK will be a horrible thing for the US."

Cracks in the friendship?

John Delury, a professor at Yonsei University's Graduate School of International Relations, said the fact that Pak brought up Trump's comments was particularly concerning, and believes that Pak's statement was likely a response to Trump bringing back the rhetoric that was common in 2017.

"It's just short of Kim Jong Un himself saying it ... but it's getting very close to the point where Kim Jong Un says kind of directly to Trump that I've lost faith in you," Delury said.

Diplomats from Pyongyang and Washington have been attempting to negotiate a trade that would see Kim give up the country's nuclear weapons and the ballistic missiles used to deliver them in exchange for relief from punishing US and United Nations sanctions that have crippled the North Korean economy.

Though North Korea first detonated a nuclear device in 2006, Pyongyang successfully test-fired missiles that could potentially hit the US mainland with a nuclear warhead for the first time in 2017 -- upping the stakes significantly and increasing the urgency to reach a peaceful solution to a decades-long struggle.

North Korea has this year continually blamed the US for the lack of progress in nuclear negotiations, singling out Secretary of State Mike Pompeo and former National Security adviser John Bolton for censure. However, Pyongyang has made a notable effort not to criticize Trump and has emphasized the importance of the two leaders' relationship.

Pak again did so Wednesday in his statement, saying he thinks "the only guarantee that deters physical conflict from flaring up in relations between the DPRK (the Democratic People's Republic of Korea, North Korea's formal name) and the US despite such a dangerous military stand-off is the close relations between the top leaders."

North Koreans are particularly sensitive to any perceived insults directed at the ruling Kim family. After former Vice President Joe Biden called Kim a dictator last month during a campaign rally, North Korea's state-run Korean Central News Agency published a commentary calling him a "rabid dog" that "must be beaten to death with a stick, before it is too late."

Even if Trump was joking when he brought back a favorite nickname he used before his budding friendship with Kim, the President may have been playing with fire.