By Debra Killalea

North Korea might be holding off on its plan to target Guam in a missile attack.

But if Kim Jong-un did decide to launch an intercontinental ballistic missile at the US territory, the Trump administration would have to decide pretty fast what action to take.

At the top of his choices would be whether to deploy the Terminal High-Altitude Area Defence system (THAAD).

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The system is designed to intercept a missile in its "terminal" phase, or the final stage, as it is coming down to hit its target and has been described as like a "bullet hitting a bullet".

North Korean media today claimed its leader had been briefed by his Missile Command on completed plans to test launch missiles and "bracket" the US Pacific territory of Guam.

But Kim stated he would watch the "foolish and stupid conduct of the Yankees" a little more before deciding whether to give an order for the missile test.

However, experts stress while North Korea does possess intercontinental ballistic missiles (ICBMs) and could use them, targeting any US territory or interests is a red line.

Brendan Thomas-Noone, a research fellow at the United States Studies Centre at the University of Sydney, said it was highly unlikely the North Koreans would fire a missile towards Guam with a nuclear warhead.

"If they were going to fire a missile towards Guam it would be a test or dummy warhead first rather than being armed," he said.

North Korean leader Kim Jong Un receives a briefing in Pyongyang. Photo / AP
North Korean leader Kim Jong Un receives a briefing in Pyongyang. Photo / AP

"It's also likely that the North Koreans would have the missile strike the waters near Guam than land on the island itself."

He said even a test would cause concern and the US would see that as a step over the line in terms of a provocation.

"Across the Trump Administration the signal has been that this would be a red line for them," he said.

"The Trump Administration would have to make the call in the moment whether to deploy THAAD and attempt to shoot it down.

"A lot of factors would go into this, regarding whether they thought it was a true threat or not and what type of response they wished to deploy."

The full THAAD includes three to six truck-mounted launchers which can carry about 50 interceptor missiles. This is backed up by a long-range radar, hailed as the world's most advanced mobile radar.

THAAD is also very powerful and has the range to be able to see deep into Chinese territory.

U.S. missile defense system called Terminal High Altitude Area Defense, or THAAD, is seen at a golf course in Seongju, South Korea. Photo / AP
U.S. missile defense system called Terminal High Altitude Area Defense, or THAAD, is seen at a golf course in Seongju, South Korea. Photo / AP

But Mr Thomas-Noone said this system was not without its risks.

"Ballistic missile defence is a game of probability and is never 100 per cent," he said.

"The more layers and systems you add, the higher chance that missiles won't make it to their target. THAAD has a decent track record in terms of testing, but it's likely the US will be deploying other capabilities like AEGIS-equipped destroyers to ensure they have multiple options."

He said there was also the risk THAAD would fail to destroy the missile, which would call into question the reliability of missile defence during a conflict situation.

'RED LINE'

Officials have told US media that satellites have observed DPRK mobile missile launcher movement, indicating an intermediate-ballistic missile may be being prepared as part of North Korea's holiday celebrations.

But Dr Euan Graham, International Security Program director at the Lowy Institute, said this didn't mean Guam was in the firing line.

North Korean leader Kim Jong Un applauded at a performance in Pyongyang. Photo / AP
North Korean leader Kim Jong Un applauded at a performance in Pyongyang. Photo / AP

Dr Graham said while the DPRK may have threatened to attack Guam it was important to read between the lines when it came to its bellicose statements.

He said the DPRK was not saying anything new and its rhetoric was always guaranteed to grab some attention.

"North Korea is looking carefully at what the US is doing," he said.

Dr Graham also pointed out Kim said he will respond only if the US does not de-escalate the situation.

Dr Graham said the rhetoric was North Korea's way of trying to have a conversation because it knew no other way to communicate.

He also pointed out the rhetoric only stepped up after Mr Trump's fire and fury comment, which resulted in North Korea threatening Guam in the first place.

The US President had been told about a Washington Post article reporting on North Korea's ability to place miniature nuclear warheads on ballistic missiles when he fired off the comment last week.

A man watches a television screen showing U.S. President Donald Trump, left, and North Korean leader Kim Jong Un during a news program at the Seoul Train Station. Photo / AP
A man watches a television screen showing U.S. President Donald Trump, left, and North Korean leader Kim Jong Un during a news program at the Seoul Train Station. Photo / AP

"North Korea best not make any more threats to the United States. They will be met with fire and fury like the world has never seen," he said.

Dr Graham said it was entirely possible the North was preparing for another launch but thought it was unlikely it would be directed at, or towards, Guam.

US Secretary of Defence James Mattis warned it would be game on if the North took such action.

"This is a pretty accurate statement from the Secretary of Defence, it's 101 self defence," he said.

"It would be a red line in the sand."

Dr Graham also said while the THAAD was in place "nothing was certain in the fog of war" and taking down an ICMB was like a "bullet hitting a bullet".

"It's not irrational for North Korea to use its weapons first," he said.

"But the thing to remember is this will ultimately lead to its destruction."

Dr Graham said he didn't think a diplomatic end was possible and thought the "phony war" would die down before it escalates once again.

'WE WILL TAKE IT OUT'

Meanwhile, Mr Mattis said he would know within moments where a North Korean missile was headed if one was launched.

A man watches a TV screen showing a local news program reporting about North Korean military's plans to launch missiles into waters near Guam, at Seoul Train Station. Photo / AP
A man watches a TV screen showing a local news program reporting about North Korean military's plans to launch missiles into waters near Guam, at Seoul Train Station. Photo / AP

"We know swiftly after it's launched where it's going to land," he said.

He also warned the US would take it out if it was headed towards US territory and Mr Trump would be the one who decided which response to take, ABC News reported.

His words came as the South Korean president said the nuclear crisis must "absolutely be solved peacefully" and there can be no US military moves without his government's consent.

Moon Jae-in said his government "will put everything on the line to prevent another war in the Korean Peninsula".

He also said the "North Korean nuclear program should absolutely be solved peacefully, and the (South Korean) government and the US government don't have a different position on this."