The new missile appears to be significantly bigger than the Hwasong-14 ICBM the North tested twice in July, the South Korean Defense Ministry said on Friday in a report carried by the South's Yonhap news agency.
On Wednesday the North performed a test launch and on Thursday released dozens of photos of the missile in the paper and online editions of the ruling party's official daily.
Pyongyang has claimed it is a fully-fledged nuclear power after its latest test.
The South Korean ministry said the new missile is bigger, more advanced, and has a domestically-made mobile launcher that, given that it can be moved, makes it harder to destroy pre-emptively.
In a tweet after the photos were published, Michael Duitsman, a researcher at the Center for Nonproliferation Studies in Monterey, California, told the Associated Press: "This is very big missile ... And I don't mean 'Big for North Korea.' Only a few countries can produce missiles of this size, and North Korea just joined the club."
A missile targeting the US would have to carry a lot of fuel, Duitsman said, noting that the new missile also appears to have a different engine arrangement and improved steering.
But weight matters too
"Initial calculations indicate the new missile could deliver a moderately sized nuclear weapon to any city on the US
mainland," Michael Elleman, a missile expert said on the resepcted 38 North think tank.
Experts are, however, still unsure whether North Korea has developed a warhead light enough to travel all the way to the west or even east coast of the US. There are also doubts as to whether Pyongyang has mastered the technology to ensure a missile survives re-entry into the Earth's atmosphere, according to a statement by South Korea's unification ministry.
The launcher issue
North Korea said in its announcement of the launch on Wednesday that the Hwasong-15 had been fired from a domestically made erector-launcher vehicle and Duitsman confirmed that the photos back the claim up.
Being able to make its own mobile launch vehicles would free the North from the need to get them from other countries, like China. This is important given the calls for a tightening of international sanctions against North Korea.
Sanctions solidarity fragmenting
As Washington urged tougher action at an emergency meeting of the UN Security Council, Russia said on Thursday that sanctions have failed while China is avoiding committing to an oil embargo.
US President Donald Trump began Thursday by complaining that China had failed to convince Kim Jong Un to back down.
"The Chinese Envoy, who just returned from North Korea, seems to have had no impact on Little Rocket Man," Trump said in a tweet. "Hard to believe his people, and the military, put up with living in such horrible conditions."
Secretary of State Rex Tillerson at a meeting with Germany's Foreign Minister Sigmar Gabriel on Thursday did press for tougher action to cut of the North's fuel supplies.
jbh/ng (AFP, AP, Reuters)