North Korean leader Kim Jong-un, in an extraordinary and direct rebuke, called U.S. President Donald Trump "deranged" and said he will "pay dearly" for his threats, a possible indication of more powerful weapons tests on the horizon.

Hours later, North Korea's foreign minister reportedly said that his country may be planning to test a hydrogen bomb in the Pacific Ocean to fulfil Kim's vow to take the "highest-level" action against the United States.

Kim, in his statement, said Trump is "unfit to hold the prerogative of supreme command of a country." He also described the U.S. president as "a rogue and a gangster fond of playing with fire."

The dispatch was unusual in that it was written in the first person, albeit filtered through the North's state media, which are part of propaganda efforts meant to glorify Kim. South Korea's government said it was the first such direct address to the world by any North Korean leader.

Kim also said Trump's comments "have convinced me, rather than frightening or stopping me, that the path I chose is correct and that it is the one I have to follow to the last." He also said he would "tame the mentally deranged U.S. dotard with fire."

Dotard means a person in a feeble or childish state due to old age. It's a translation of a Korean word, "neukdari," which is a derogatory reference to an old person.

Early Friday morning, Trump called Kim a "madman" and said he "would be tested like never before" in a comment on Twitter.

Kim Jong Un of North Korea, who is obviously a madman who doesn't mind starving or killing his people, will be tested like never before! —@realDonaldTrump

Weapons testing could increase

Some analysts saw a clear announcement that North Korea would increase its already brisk pace of weapons testing, which has included missiles meant to target U.S. forces throughout Asia and the U.S. mainland.

"I will make the man holding the prerogative of the supreme command in the U.S. pay dearly for his speech calling for totally destroying the DPRK," said the statement carried by North's official Korean Central News Agency on Friday morning.

DPRK is the abbreviation of the country's official name, the Democratic People's Republic of Korea.

North Korean Foreign Minister Ri Yong Ho told reporters on the sidelines of a United Nations gathering that his country's response "could be the most powerful detonation of an H-bomb in the Pacific," according to South Korea's Yonhap news agency.

'Unprecedented rude nonsense'

Ri reportedly added that "We have no idea about what actions could be taken as it will be ordered by leader Kim Jong-un."

Such a test would be considered a major provocation by Washington and its allies.

North Korean Foreign Minister Ri Yong Ho threatened a hydrogen bomb test in the Pacific. (Mark Schiefelbein/Associated Press)

Japanese Defence Minister Itsunori Onodera noted such a test could mean a nuclear-armed missile flying over Japan. He said North Korea might conduct an H-bomb test with a medium-range or intercontinental ballistic missile, given its recent advances in missile and nuclear weapons development.

"We cannot deny the possibility it may fly over our country," he said.

Potential danger to shipping, aircraft

Vipin Narang, a nuclear strategy expert at MIT, said that such a test could pose a danger to shipping and aircraft, even if the North declared a keep-out zone.

"And if the test doesn't go according to plan, you could have population at risk, too," he said. "We are talking about putting a live nuclear warhead on a missile that has been tested only a handful of times. It is truly terrifying if something goes wrong."

The statement by Kim Jong-un responded to Trump's combative speech at the UN General Assembly on Tuesday where he mocked Kim as a "rocket man" on a "suicide mission," and said that if "forced to defend itself or its allies, we will have no choice but to totally destroy North Korea."

U.S. president threatens to destroy North Korea in UN speech 1:14

Kim characterized Trump's speech to the world body as "unprecedented rude nonsense."

Response 'beyond his expectation'

He said Trump's remarks "have convinced me, rather than frightening or stopping me, that the path I chose is correct and that it is the one I have to follow to the last."

Kim said he is "thinking hard" about his response and that Trump "will face results beyond his expectation."

North Korean leader Kim Jong-un delivered a statement in response to U.S. President Donald Trump's speech to the United Nations, calling Trump "deranged". (Korean Central News Agency/Korea News Service via AP)

Kim Dong-yub, a former South Korean military official who is now an analyst at Seoul's Institute for Far Eastern Studies, said Kim's statement indicated that North Korea will respond to Trump with its most aggressive missile test yet. That might include firing a Hwasong-14 intercontinental ballistic missile over Japan to a range of around 7,000 kilometres to display a capability to reach Hawaii or Alaska.

The statement will further escalate the war of words between the adversaries as the North moves closer to perfecting a nuclear-tipped missile that could strike America.

'Reckless provocation'

In recent months, the North has launched a pair of still-developmental ICBMs it said were capable of striking the continental United States and a pair of intermediate-range missiles that soared over Japanese territory. Earlier this month, North Korea conducted its sixth and most powerful nuclear test to date drawing stiffer UN sanctions.

U.S. President Donald Trump appeared on a screen in Tokyo on Wednesday, as he threatened North Korea in an address to the United Nations. (Eugene Hoshiko/Associated Press)

South Korea called Kim Jong-un's rebuke a "reckless provocation" that would deepen his country's international

isolation and lead to its demise.

South Korea's Unification Ministry spokesman Baik Tae-hyun told reporters Friday that North Korea must immediately stop such provocations and return to talks on nuclear disarmament.

'Extremely serious'

During a news conference Thursday at the UN, Prime Minister Justin Trudeau said he considers the situation in North Korea "extremely serious."

"The North Korean regime represents a threat to not just regional security, but global peace."

Canadian Prime Minister Justin Trudeau said North Korea threatens global peace. (Adrian Wyld/Canadian Press)

He said the development of nuclear weapons by the regime "represents something that all countries in the world should be seized with and concerned about."

Trudeau said he recently spoke with the South Korean president about the challenges his country is facing.

The prime minister said that, among other issues, the pair talked about the "levers available to neighbouring countries," including China and Russia, to try to reduce the threat and de-escalate the situation in North Korea.