President Donald Trump warned North Korea not to underestimate America's military capabilities and said Kim Jong-un's nuclear weapons programme was making the North Korean leader and his regime less safe.
“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,” Mr Trump told South Korea’s national assembly during his five-nation Asian tour.
On Tuesday he hit more conciliatory tones on North Korea after a summit with South Korean leader Moon Jae-in, but his speech to the national assembly, the first by a US leader to the Seoul parliament for 24 years, was uncompromising.
Mr Trump did hold out the prospect of a way forward, but only under very tough conditions.
“We will offer a path to a much better future. It begins with an end to the aggression of your regime, a stop to your development of ballistic missiles, and complete, verifiable and total denuclearisation,” he said.
"The weapons that you are acquiring are not making you safer, they are putting your regime in grave danger. Every step you take down this dark path increases the peril you face," Mr Trump said, in a direct message to Mr Kim.
“The world cannot tolerate the menace of a rogue regime that threatens it with nuclear devastation,” Mr Trump said.
In his speech that received a standing ovation, he painted a picture of a cruel and backward regime, and contrasted North Korea with the richer South.
“North Korea is a country ruled by a cult,” he said, going on to describe it as a “hell no person deserves.”
‘Taken away in a bucket’
Earlier Mr Trump was forced to cancel a surprise visit to the demilitarised zone because of fog. He had denied he was going there but then went anyway, however his helicopter was forced to turn back.
Mr Trump was speaking shortly before leaving for Beijing and had strong words for China, North Korea's main trading partner and ideological ally, which he has occasionally criticised for not doing enough to pressure Pyongyang.
“To those nations that choose to ignore this threat or, worse still, to enable it, the weight of this crisis is on your conscience,” he said.
"We call on every nation, including China and Russia, to fully implement UN Security Council resolutions, downgrade diplomatic relations with the regime, and sever all ties of trade and technology."
There was a major security lockdown around the St Regis hotel in Beijing shortly before his anticipated arrival, with a whole city block surrounded by security fencing, scores of soldiers and People’s Armed Police on patrol.
China’s president Xi Jinping is likely to repeat the line that Beijing it is doing all it can to rein in its ally, but Mr Trump will reiterate calls for China to stop providing oil and fuel.
In one section of his speech in Seoul, during his description of North Korea’s dystopia, Mr Trump told of how “one woman’s baby born to a Chinese father was taken away in a bucket. ... So why would China feel an obligation to help North Korea?”