President Donald Trump has delivered a sharp warning to North Korean leader Kim Jong Un, telling him the weapons he is acquiring "are not making you safer. They are putting your regime in grave danger."
In a speech delivered hours after he aborted a visit to the heavily fortified Korean demilitarised zone due to bad weather, Mr Trump called on all nations to join forces "to isolate the brutal regime of North Korea - to deny it any form of support, supply, or acceptance".
"Today, I hope I speak not only for our countries, but for all civilised nations, when I say to the North: Do not underestimate us. And do not try us.
"We will defend our common security, our shared prosperity, and our sacred liberty," he told South Korean lawmakers.
Mr Trump had been scheduled to make the unannounced early morning trip to the demilitarised zone - or DMZ - amid heightened tensions with North Korea over its nuclear program.
The Marine One presidential helicopter left Seoul at daybreak and flew most of the way to the DMZ but was forced to turn back just five minutes out due to poor weather conditions.
Reporters travelling in a separate helicopter as part of the president's envoy saw fog through the windows, and weather reports from near the heavily fortified border showed misting conditions and visibility below one mile.
Pilots, officials said, could not see the other helicopters in the air.
White House press secretary Sarah Huckabee Sanders said the president was disappointed he couldn't make the trip. "I think he's pretty frustrated," she told reporters. "It was obviously something he wanted to do."
Before he left for Asia, a White House official had ruled out a DMZ visit for Mr Trump, claiming the president didn't have time on his schedule and that DMZ visits have become a little cliche.
But Ms Sanders said the visit had been planned well before Trump's departure for Asia. The trip was kept secret for security reasons, she said.
Mr Trump had been scheduled to make the visit with South Korean President Moon Jae-in, who travelled separately and landed about a 20-minute drive from the DMZ.
Ms Sanders said the military and the US Secret Service had deemed that landing would not be safe, and Mr Trump deferred to them.
After returning to Seoul, administration officials had hoped they might be able to wait out the bad weather and make a second landing attempt.
At the US Army's Yongsan Garrison landing zone, White House Chief of Staff John Kelly and Ms Sanders frequently glanced up at the clouds to see if the sky was clearing. But time would not allow it.
The aborted visit came hours before Mr Trump addressed the South Korean National Assembly before closing out his two-day visit to the nation and heading to his next stop, Beijing.
Visiting the border that has separated the North and South for 64 years has become something of a ritual for US presidents trying to demonstrate their resolve against North Korea's ever-escalating aggression.
Every American president since Ronald Reagan, save for George HW Bush, has made the trip, peering across the barren north through binoculars, hearing broadcast propaganda and reaffirming their commitment to standing with the South.