North Korea has claimed that a ballistic missile test it carried out on Sunday was a new type of rocket capable of carrying a large nuclear warhead.
South Korea's military said it could not yet verify the North's claims, but the North's missiles did appear to be able to leave and re-enter the atmosphere, which is crucial to developing intercontinental ballistic missiles.
North Korea has carried out several missile tests this year - mostly unsuccessful but still in contravention of un sanctions, sparking international alarm and raising tensions with the US.
On Sunday North Korea carried out a missile test, firing a ballistic missile that landed in the sea near Russia. Moscow responded saying provocations by North Korea are tantamount to hostility and Russia is ready for all-out war.
However, North Korea's supreme leader accused the United States of "browbeating" countries that "have no nukes" and warned Washington not to misjudge the reality that its mainland is in the North's "sighting range for strike".
Meanwhile, Australian Prime Minister, Malcolm Turnbull, expressed his country's support for the United States in its policy on North Korea.