Donald Trump has said that thanks to him, the US's nuclear arsenal is "far stronger and more powerful than ever before," a day after he dramatically upped the stakes in the war of rhetoric with North Korea and threatened "fire and fury" against the isolated country.

Mr Trump took to his favoured venue Twitter to communicate this morning that his first act as President was to strengthen the US nuclear arsenal. However, his first act in office on 20 Janurary according to the White House website was an executive order regarding "minimising the economic burden" of patients under Obamacare.

He added that "there will never be a time when" the US is not the "most powerful" nation on the planet.

However, in a move that has become somewhat characteristic of the Trump administration, Secretary of State Rex Tillerson had a somewhat contradictory message after Mr Trump's "fire and fury" comment.

Mr Tillerson travelled unexpectedly to the US territory of Guam earlier today after North Korea threatened to attack the small Pacific island nation after news of Pyongyang's ability to build a nuclear warhead capable of fitting inside a missile became known.

The typically tacit Secretary of State addressed the media while on his plane: "I do not believe that there is any imminent threat...Americans should sleep well at night".

Guam, approximately 2,200 miles (3540 km) southeast of North Korea, has two US military bases and is the home port for nuclear submarines.

Guamanians, who do not vote for US presidents but have party delegates in Washington, DC, have been threatened before by Kim Jong-un.

In 2013 and 2016, the mercurial leader warned that US bases in the Pacific would face attack.

As Mieke Eoyang, Vice President for the National Security Program at DC-based think tank Third Way, pointed out on Twitter - North Korea lacks "second strike" capabilities should the US respond to any possible attack on US territories, Hawaii, or even South Korea and Japan.

Congress is currently in recess but several members have responded to Mr Trump's comments in the last 24 hours.

Chair of the Senate Armed Services Committee Senator John McCain told an Arizona radio station that "the great leaders I've seen don't threaten unless they're ready to act and I'm not sure President Trump is ready to act."

In pictures: North Korea military drill Show all 8 1 /8 In pictures: North Korea military drill In pictures: North Korea military drill North Korea's leader Kim Jong Un watches a military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video

While Senator Chuck Schumer called the President's comments "reckless," colleague Lindsey Graham told CBS that Mr Trump "is going to pick homeland defence over regional stability and he has to. ...We've failed for 30 years, it's time to try something new."

Despite Mr Trump and Mr Kim's back-and-forth fiery rhetoric, experts say that the likelihood of North Korea actually attacking Guam is quite low.

Scott Snyder, Senior Fellow for Korea Studies and Director of the Program on U.S.-Korea Policy at the Council on Foreign Relations told The Independent that "North Koreans usually [operate] based on a kind of guerilla approach. It is very unusual for them to pre-announce their targets. The statement is a response to US threats that actually tries to also direct US attention to the source of vulnerability in Guam."

The US can "launch nuclear-capable flyovers" to the Korean peninsula but a North Korean attack there - in theory - could disable that capability.

Mr Snyder said that if Pyongyang attacks Guam, it would be "suicidal, and Kim Jong-un is not suicidal".

But, the threat is not an empty one despite the small chance of follow-through.

"If you are a US security planner...you still have to prepare for that possibility," Mr Snyder noted.

Matthew Wallin, Senior Fellow at American Security Project, told The Independent that he also does not think North Korea will attack Guam because it would "end in the destruction of the regime".

The whole reason Mr Kim developed nuclear weapons is to preserve his regime, said Mr Wallin.

Rex Tillerson explains Donald Trump's North Korea comments

The other issue at hand is US-South Korea relations.

South Korean President Moon Jae-in has expressed in the past a hesitation for military action against North Korea given the short distance Pyongyang and Seoul.

Mr Moon, elected only in May 2017, also campaigned on a Sunshine Policy, advocating for exhausting all non-military options for better relations with the North.

"North Korea keeps popping [Mr Moon's] trial balloons," however, said Mr Snyder. The South Korean leader has proposed a joint Olympic team, trade corridors, and humanitarian aid - all dismissed by Pyongyang.

In a recent meeting between the two foreign minister, the North Korean minister said the South's efforts at better relations were "insincere".

Mr Snyder said that despite this, Mr Moon essentially "embedded himself deeply in the US-Korea alliance" once he took office and came to meet Mr Trump in person.

South Korea supports any sanctions against North Korea, but should the "US toolkit" be reduced to only military options it could face serious opposition from Seoul according to Mr Snyder.

However, "we are not at the point yet" that the opposition would be drowned out because the US feels an direct, imminent threat from Pyongyang.

Mr Wallin argues that going forward diplomatic efforts should focus on pressuring China more than any other matter, getting it to deal with its regional issue and aid to North Korea.

The US also "needs to provide an offramp for de-escalation and denuclearisation that will allow North Korea to save face and not fear for its own survival," he said.

Setting an example through tamping down the Trump administration's fiery rhetoric on Iran would help to show that survival of a denuclearised power is possible, Mr Wallin said.