US President Donald Trump says "let's see" about what North Korea does to Guam
Kim Jong-un has ordered North Korea's military scientists to boost production of more effective missiles that can be launched faster and hidden more easily, making the country less vulnerable to a pre-emptive strike.
Kim visited the North Korean Chemical Material Institute of the Academy of Defence Science recently, according to a statement from the government-run Korean Central News Agency (KCNA).
"He instructed the institute to produce more solid-fuel rocket engines and rocket warhead tips by further expanding engine production process and the production capacity of rocket warhead tips and engine jets by carbon/carbon compound material," the statement read.
Kim Jong Un, center, visits the Chemical Material Institute of Academy of Defense Science at an undisclosed location in North Korea. Photo / AP
The order to create more solid-fuel rocket engines is significant because the fuel is built into these weapons and they are ready to fire at any moment. They can be launched much faster than liquid-fuel rockets, which have to be loaded with fuel before being fired, a process that can take up to an hour.
The solid-fuel rocket engines essentially mean North Korea is more competitive in the event of a nuclear war because it is less vulnerable to a pre-emptive strike from adversaries, such as the United States, which can view missile movements via satellite.
During his visit to the institute, the date of which was not made clear in the KCNA statement, Kim praised its scientists as "patriotic" and "unassuming heroes" who were at the "cutting edge" of defence technology.
The solid-fuel rocket engines were put on display in April during an extravagant procession in Pyongyang to celebrate the birthday of North Korea's founding father, Kim Il-sung.
Tensions between the rogue state and its enemies, South Korea and the US, have been heightened in recent months, since it was revealed that North Korea had developed its weapons to the point where the US mainland was within striking distance.
North Korean leader Kim Jong-un visits the Chemical Material Institute of the Academy of Defence Science. Photo / AP
As a result, President Donald Trump vowed to rain "fire and fury" upon North Korea if it threatened the US or any of its allies.
Trump told supporters in a rally in Phoenix, Arizona, on Tuesday night that his forceful warning to Kim was having an effect.
"Some people said it was too strong. It's not strong enough," he said.
"But Kim Jong-un, I respect the fact that I believe he is starting to respect us. I respect that fact very much.
Kim Jong-un ordered a boost in production for solid-fuel rocket engines and rocket warhead tips. Photo / AP
"And maybe, probably not, but maybe something positive can come about."
Secretary of state Rex Tillerson also acknowledged that the tough United Nations sanctions the US had helped impose on North Korea were changing its behaviour.
"I am pleased to see that the regime in Pyongyang has certainly demonstrated some level of restraint that we've not seen in the past," he said.
South Korea and the US are currently engaged in a 10-day military drill known as Ulchi-Freedom Guardian, which has sparked the ire of Kim.
Kim Jong-un examines the latest in North Korean military technology. Photo / AP
The North sees the massive land, air and sea war games as a provocation, because it believes it is a way for the South to prepare for an invasion.
Washington and Seoul, which will each deploy tens of thousands of troops for the exercise, maintain it is a defensive manoeuvre and a response to North Korean aggression.
Past drills are believed to have included simulated "decapitation strikes", which see soldiers carry out trial operations to kill Kim and his top generals.
