Donald Trump has said that the US is ready with a "military option" to end the crisis with North Korea in the latest chapter of the escalating rhetoric between the two countries.

"We are totally prepared for the second option, not a preferred option," Mr Trump said at a White House news conference alongside Spain's Prime Minister Mariano Rajoy. "But if we take that option, it will be devastating, I can tell you that, devastating for North Korea. That's called the military option. If we have to take it, we will."

The President proceeded to say that North Korean Foreign Minister Ri Yong-ho – who said over the weekend that it was "inevitable" that North Korean rockets would hit the US mainland as part of its expanding nuclear ambitions – was acting "very badly, saying things that should never be said". Mr Ri had also claimed that Mr Trump had issued a declaration of war in tweeting that North Korean leaders "won't be around much longer" if they keep on threatening the US.

Mr Trump's threats are just the latest in a series of insults hurled between him and North Korean leader Kim Jong-un. The President gave a particularly feisty speech during his first address to the United Nations General Assembly last week, calling Mr Kim "Rocket Man", and saying he was on a "suicide mission". Mr Kim followed up by calling Mr Trump a "dotard" – a phrase used to describe an elderly, senile person – and a "frightened dog".

"I will surely and definitely tame the mentally deranged US dotard with fire," Mr Kim said in an unprecedented statement addressing a foreign leader.

Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Show all 6 1 /6 Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Photos released by North Korea show Kim Jong-un talking to subordinates next to a device thought to be the new thermonuclear weapon. There is no way of independently verifying the pictures STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb North Korea claims it has successfully tested an advanced hydrogen bomb which could be loaded onto an intercontinental ballistic missile AFP/Getty Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A diagram on the wall behind Mr Kim shows a bomb mounted inside a cone STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb North Korean leader Kim Jong-Un (C) attending a photo session with participants of the fourth conference of active secretaries of primary organisations of the youth league of the Korean People's Army (KPA) in Pyongyang STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A new stamp issued in commemoration of the successful second test launch of the "Hwasong-14" intercontinental ballistic missile KCNA via Reuters Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A new stamp issued in commemoration of the successful second test launch of the "Hwasong-14" intercontinental ballistic missile KCNA via Reuters

Those statements provoked a rebuke from Mr Trump, who said via Twitter that Mr Kim doesn't care about "starving or killing his people" and said that the North Korean leader would "be tested like never before!"

North Korea, which conducted its sixth and most powerful nuclear weapon test earlier this month, has threatened to conduct another nuclear test, and has said that they've considered doing so in the Pacific Ocean. Doing so would most likely require North Korea to shoot a missile over Japan, leading to a potential catastrophe there if there was a malfunction in the missile.

"It could be the most powerful detonation of an H-bomb in the Pacific," Mr Ri said last week of his country's potential response to Mr Trump. "We have no idea about what actions could be taken as it will be ordered by leader Kim Jong-un."

The top US military officer said on Tuesday that any such action would be "incredibly provocative".

Marine Corps General Joseph Dunford, chairman of the US Joint Chiefs of Staff, told a Senate Armed Services Committee hearing: “It would be an incredibly provocative thing for them to conduct a nuclear test in the Pacific as they have suggested, and I think the North Korean people would have to realise how serious that would be, not only for the United States but for the international community”.

However, despite the increased tension, the US has not detected any change in North Korea's military posture reflecting an increased threat, according to General Dunford.

“While the political space is clearly very charged right now, we haven't seen a change in the posture of North Korean forces, and we watch that very closely,” he said.

In terms of a sense of urgency, “North Korea certainly poses the greatest threat today,” General Dunford testified.

The escalation in rhetorical warfare has some experts concerned that, in addition to raising the bar of insults, the two leaders may raise expectations that they could actually act after puffing their chests.

"I think this will lead to something in the coming days," Gi-wook Shin, the director of the Walter H Shorenstein Asia-Pacific Research Centre at Stanford University, told The Independent. "That's why I'm concerned, that it might be more than an escalation of rhetoric. There may be escalation of expectations."

Tensions between Mr Trump and Mr Kim have become increasingly worrisome over recent months, as North Korea has tested its nuclear weapons and its intercontinental ballistic missile (ICBM) systems.

In response to those tests – which has included an ICMB that experts suggest has the capability to make it to the US homeland – the US and the UN have imposed strict sanctions on North Korea, further isolating the country from the financial world. Although China is a major trading partner for North Korea, the national bank there has instructed its banks to honour those sanctions, and has threatened retaliation if financial institutions continue business as usual with North Korea individuals and companies.

General Dunford said Pyongyang will have a nuclear-capable intercontinental ballistic missile “soon”, and it was only a matter of a “very short time”.

“We clearly have postured our forces to respond in the event of a provocation or a conflict,” the general said, adding that the United States has taken “all proper measures to protect our allies” including South Korean and Japan.

Elsewhere, South Korean MP Lee Cheol-uoo, briefed by the country's spy agency, said North Korea was bolstering its defences by moving aircraft to its east coast and taking other measures after the flight by US bombers. Mr Lee said the United States appeared to have disclosed the flight route intentionally because North Korea seemed to be unaware.

The United States has also imposed sanctions on 26 people as part of its non-proliferation designations for North Korea and nine banks, including some with ties to China, the US Treasury Department's Office Of Foreign Assets Control Sanctions said.