US President Donald Trump arrived in China on Wednesday seeking help to rein in North Korea.

:: US President Donald Trump arrived in China on Wednesday seeking help to rein in North Korea after warning the North’s leader that the nuclear weapons he is developing “are not making you safer, they are putting your regime in grave danger.”

Trump used some of his toughest language yet against North Korea in a wide-ranging address in Seoul that lodged specific accusations of chilling human rights abuses. He called on countries around the world to isolate Pyongyang by denying it “any form of support, supply or acceptance.”

“Do not underestimate us and do not try us,” Trump told North Korea as he wrapped up a visit to South Korea with a speech to the National Assembly before heading to Beijing, where he was making his first official visit.

Trump painted a dystopian picture of the reclusive North, saying people were suffering in “gulags” and some bribed government officials to work as “slaves” overseas rather than live under the government at home. He offered no evidence to support those accusations.

Trump’s return to harsh, uncompromising language came a day after he appeared to dial back the bellicose rhetoric that had fueled fears across east Asia of the risk of military conflict. On Tuesday, Trump had even offered a diplomatic opening to Pyongyang to “make a deal.”

He went mostly on the attack in Wednesday’s speech but did promise a “path to a much better future” if North Korea stopped developing ballistic missiles and agreed to “complete, verifiable and total denuclearization” – something Pyongyang has vowed never to do.

“We will not allow American cities to be threatened with destruction. We will not be intimidated,” he told South Korean lawmakers. “And we will not let the worst atrocities in history be repeated here, on this ground we fought and died to secure.”

The North defends its nuclear weapons and missile programs as a necessary defense against what it says are US plans to invade. The United States, which has 28,500 troops in South Korea, a legacy of the 1950-53 Korean war, denies any such intention.

“The world cannot tolerate the menace of a rogue regime that threatens it with nuclear devastation,” Trump said, speaking as three US aircraft carrier groups sailed to the Western Pacific for exercises – a rare show of such US naval force in the region.