A US Air Force B-1B Lancer bombers sits at Andersen Air Force Base in Guam before conducting a mission over South Korea.
"North Korea's actions are a threat to our allies, partners and homeland," Gen. Terrence O'Shaughnessy, Pacific Air Forces commander, said.
"Let me be clear, if called upon we are trained, equipped and ready to unleash the full lethal capability of our allied air forces," the general said.
South Korean and Japanese warplanes as well as US F-16 fighters joined the US bombers for parts of Friday's mission, during which the bombers used inert weapons to practice attacks on a South Korea firing range.
The B-1 flight over South Korea follows a familiar pattern. Friday's was at least the sixth since April, all to show US resolve in the face of North Korean missile tests.
Pressure not working on North Korea
But they don't appear to have given Pyongyang any pause in building its missile program, with last Tuesday's test apparently its most successful to date.
"There is no amount of military pressure alone that will compel Kim Jong Un to volunteer to eliminate his nuclear and missile programs," Adam Mount, a senior fellow at the Center for American Progress, said after B-1 flights in late May.
Mount told CNN then that the US hasn't given North Korea any "red lines" it cannot cross, meaning the Kim regime has no reason to stop moving ahead with its nuclear missile program.
"I don't draw red lines," US President Donald Trump said Thursday in reaction to the North Korean ICBM test.
"I have some pretty severe things that we are thinking about. That doesn't mean we are going to do it," Trump said.
Calling Washington's bluff
Robert Ross, a Boston College professor and East Asia security policy expert, foreshadowed the current situation when he spoke to CNN in early June.
"North Korea will call our bluff, the US will draw back from using military force, and North Korea will continue to develop their nuclear program," Ross said.
Experts have pointed to China, North Korea's longtime ally, as possibly having enough leverage to rein in Pyongyang.
But US military actions in the South China Sea are antagonizing Beijing.
China called the action "a serious political and military provocation." The US "stirs up trouble" and runs "in the opposite direction from countries in the region who aspire for stability, cooperation and development," a statement from China's Foreign Ministry said.
China's Foreign Ministry said it had no specific information on that flight, but added, "we are firmly opposed to saber-rattling that harms China's sovereignty and security by certain countries on the pretext of freedom of navigation and overflight."
Thursday's flight of B-1s over the East and South China seas was a two-part mission, the US Air Force said.
In the first part of Thursday's mission, the B-1s were joined by two Japanese F-15 fighters and carried out a cooperative mission over the East China Sea -- an area both Japan and China claim as their own.
The Japanese Air Self Defense Force claims that the mission was not intended to send a message to any specific country despite previous face-offs in the East China Sea with Chinese ships and warplanes.
CNN's Eric Cheung, Steven Jiang and Barbara Starr contributed to this report.