It comes after Pyongyang released propaganda images showing Kim galloping on horseback through snowy mountains on his way up to Mount Paektu.
The Hwasong-15 had its first and only test launch in 2017, but the missile's potency was not immediately clear.
The RS-28 Sarmat is reportedly able to carry a nuclear payload capable of destroying an area the size of Texas.
General Terrence O'Shaughnessy said the U.S. now faces "adversaries that are actually able to reach out and touch us."
President Vladimir Putin has ordered over a dozen regiments to finish upgrading their Topol missile systems this year, among other military updates.
The RS-28 Sarmat could be seen taking flight as both the Russian and U.S. leaders discussed an "arms race."
The tests come as Russian President Vladimir Putin revealed new nuclear missiles and Moscow's relationship with the West took another major blow.
The Hwasong-14 and Hwasong-15 put the U.S. in North Korea's trajectory, so how easily will Kim Jong Un give them up?
Russia's new RS-28 Sarmat intercontinental ballistic missile is allegedly capable of wiping out Texas, but Putin's demonstration took aim elsewhere.
Russia's ambassador to North Korea said Moscow's nuclear-armed neighbor would consider an attempt to stop oil flow to be a "declaration of war."
"It will be a very, very kinetic, physical, violent fight over some really, really tough ground, and everybody is going to have to be mentally prepared," Marine Corps Commandant General Robert Neller said.
North Korea said it was able to build nuclear bombs and intercontinental ballistic missiles because it trusts no one but itself.
A man who claimed to be a bodyguard to Kim Jong Il said his youngest son was "angry," "stressed" and "his personality was explosive."
Kim Jong Un's lack of response to Trump's "nuclear button" tweet may mean North Korea is serious about peace talks. But is the U.S.?
Nearly a year after Trump took office, 17 former nuclear launch officers said, "The reality of this presidency is worse than we feared."
Kim Jong Un is "trying to make himself the reincarnation of Kim Il Sung, who was really beloved by the North Koreans."
One year ago today, Donald Trump vowed North Korean supreme leader Kim Jong Un would never launch an intercontinental ballistic missile.
On January 1, 2017, Kim Jong Un promised to deliver missiles that could hit the U.S. Trump said it wouldn't happen. It did.
The test was unusual in that it was conducted in the dead of night.
Kim's public appearances are regularly recorded in a special section of the ruling party's newspaper, titled Supreme Leader's Activities.
Missiles that F-35 stealth fighters already carry need only slight tweaks to be able to target ICBMs, an aerial combat expert says.
In its latest commentary, North Korea's official news agency warned that "the right to preemptive attack is not exclusive to the U.S."