Does Donald Trump have the nuclear launch codes and what has the US president said about North Korea?
AS President of the United States and Commander-in-Chief of its military, Donald Trump has the biggest nuclear arsenal in history at his disposal.
Trump has made frequent references to America's nuclear capability and has famously said the power he wields is "very, very scary". But is he the only man authorised to press the button?
Could President Trump start World War 3?
Trump was given access to the launch codes in one of his first tasks as Commander-in-Chief.
Reports said he always carries the so-called Gold Codes on his person, printed on a credit-card sized piece of plastic nicknamed "the biscuit".
If he is away from the White House, Trump will be accompanied by a military aide who carries the "nuclear football" - a briefcase containing a mobile hub linked to the strategic defence system.
Once a launch has been ordered, a short code is sent to sites where crews will authenticate them before launching.
Trump previously insisted he would not recklessly launch nuclear action, but days into 2018, the President warned North Korea that he had a "bigger and more powerful nuke button".
If President Trump were to order an attack, no one can stop it – the military will simply confirm the codes and fire.
Officers may resign, but the attack would still go ahead.
Bruce G. Blair, a former Minuteman missile-launch officer and research scholar at Princeton told Bloomberg: "The Commander-in-Chief’s power is clear: He or she has sole authority to use nuclear weapons.
"Before initiating military action, the president convenes a conference with military and civilian advisers in Washington. If travelling, the President is patched in on a secure line.
"The consultation lasts as long as the president wishes, but if enemy missiles are heading toward the US and the president must order a counter strike, the consultation may last just 30 seconds."
Once he has ordered a launch, a short code is transmitted to launch sites – where crews will then authenticate them against sealed codes provided by the National Security Agency, before launching.
What has Trump and his administration said about North Korea?
Trump has announced he will hold landmark talks with Kim Jong-un later this month while also building bridges at home.
In last night's State of the Union address, the US President revealed news of a two-day summit with the North Korean leader in Vietnam on February 27-28.
The "peace" talks with the North Korean leader are part of an effort to persuade Kim to give up his deadly nuclear weapons arsenal.
They will come after the United Nations accused the rogue state of hiding its nuke stockpile from inspectors.
Speaking to Congress, the President said that continued outreach to Kim and their first meeting last June in Singapore opened a path to peace.
But there is not yet a concrete plan for how denuclearisation could be implemented.
President Trump said on Tuesday night: ";As part of a bold new diplomacy, we continue our historic push for peace on the Korean Peninsula."
Denuclearising North Korea is something that has eluded the US for more than two decades.
Director of National Intelligence Dan Coats told Congress last week that American intelligence officials do not believe Kim will eliminate his nuclear weapons.
Nor will Kim scrap his country's capacity to build more - because he believes they are key to the survival of the regime.
Are there efforts to block Trump from having the power to launch a nuclear weapon?
Defence Secretary Jim Mattis played down Mr Trump's role in nuclear launch decision-making, telling reporters: “I’m the President’s principal adviser on the use of force.”
Asked whether he was happy with the current system as it was, Mattis simply said: “I am.”
If Trump did move to launch a nuclear strike the US military would be likely to demand a reasonable and rational explanation for the attack.
How big is America's nuclear arsenal?
America currently has about 900 active nuclear warheads.
The strategic nuclear warheads are deployed on intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and strategic bomber aircraft.
The State Department announced in April 2015 that approximately 2,500 warheads are retired and await dismantlement.
The United States and Russia account for 93 per cent of nukes. Since their peak in the mid-1980s, global arsenals have shrunk by more than two-thirds.
More countries have given up weapons and programs in the past 30 years than have tried to acquire them.
What has Trump said about nuclear war?
Trump implied he remains ready to press launch a nuclear attack on North Korea, in a tweet earlier this year.
He said: "Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!"
This came as no surprise, as in his first TV interview as President, Trump said he would have no qualms about launching a nuclear strike.
He told ABC’s David Muir: “When they explain what it represents and the kind of destruction that you’re talking about, it is a very sobering moment.
"It's very, very, very scary in a sense."
He added: "I have confidence I'll do the right thing, the right job, but it's a very scary thing."
Trump has gone back and forth on the nuke issue, but had suggested while campaigning that South Korea and Japan should be allowed to acquire nuclear arms.
He said: "It's not like, gee whizz, nobody has them. So, North Korea has nukes. Japan has a problem with that.
"I mean, they have a big problem with that. Maybe they would, in fact, be better off if they defend themselves from North Korea."
When asked to clarify if he meant nuclear weapons, Trump responded: "Including with nukes, yes, including with nukes."
Trump later said he never said Japan should get nuclear weapons.
In February 2017, Trump stressed he intended for the US nuclear arsenal to stay "top of the pack".
He added: “I am the first one that would like to see ... nobody have nukes, but we’re never going to fall behind any country even if it’s a friendly country, we’re never going to fall behind on nuclear power."
In the event of nuclear war, the US has large fall-out shelters which are being dusted off for the first time since the fall of the Soviet Union.
As tensions escalated over the summer with North Korea and Kim Jong-un, Trump famously warned he would retaliate with "fire and fury" if North Korea continued to threaten the US.
In October 2017, Trump sent nuclear bombers to fly towards North Korea in a dramatic show of force.
What has Kim said about nuclear war?
North Korean despot Kim Jong-un proudly declared his country has become a nuclear state after a launching a new missile.
The weapon, launched on November 28, is capable of hitting anywhere on earth and is the latest in a long line of test rockets to be deployed.
State television broadcast a photo of Kim's signed order where he wrote: "Test launch is approved. Taking place at the daybreak of Nov. 29! Fire with courage for the party and country!"
Pyongyang said the new powerful missile - equipped with a "super-large heavy warhead" - reached an altitude of around 2,780 miles - more than TEN TIMES the height of the international space station - and flew 600 miles during its 53-minute flight.
The rogue leader used his 2018 New Year's address to warn President Trump, the US was within reach of his nuclear weapons. He added: "The nuclear button is always on my table."
US Defence Secretary Jim Mattis said North Korea's missiles can "threaten everywhere in the world".
What has Vladimir Putin said about nuclear war?
In March 2018, Vladimir Putin boasted Russia had developed an ICBM invulnerable to missile defence systems.
The newly developed intercontinental ballistic rocket has "unlimited range", the Russian leader said in his state of the nation address in Moscow.
Footage shown during his speech apparently showed the new missiles heading toward the United States as he promises to "neutralise" America's missile defence.
Putin, 65, also announced a web contest to name a new, high-speed underwater drone which carries nuclear warheads and can destroy aircraft carriers and coastal facilities.
And Russia has apparently tested a new heavy intercontinental ballistic missile, called Sarmat, whose range and number of warheads exceeding its predecessor.
"Russia remained a nuclear power but no one wanted to listen to us," Putin told lawmakers. "Listen to us now."
Latest Donald Trump News
What's the latest?
Trump has insisted he "had to walk"; from his summit with Kim Jong-un after the pair failed to agree a nuke deal and their lunch was dramatically cancelled.
The leaders scrapped a planned signing ceremony as their second day of crunch talks in Hanoi, Vietnam, ended without an agreement on how to denuclearise the Korean peninsula.
At a press conference, the US President said the despot refused to dismantle North Korea's Yongbyon nuclear complex and wanted the sanctions imposed on his crackpot regime lifted.
The brash New Yorker said that the North Korea leader wants to "denuke a portion" of his country - which was another point of contention for the US administration.
He added that Kim promised that he would not resume testing of ballistic missiles despite the talks breaking down.