WASHINGTON - President Donald Trump said on Tuesday that Chinese efforts to persuade North Korea to rein in its nuclear programme have failed, ratcheting up the rhetoric over the death of an American student who had been detained by Pyongyang.
Trump had held high hopes for greater co-operation from China to exert influence over North Korea, leaning heavily on Chinese President Xi Jinping for his assistance.
The two leaders had a high-profile summit in Florida in April and Trump has frequently praised Xi and resisted criticising Chinese trade practices.
"While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out. At least I know China tried!" Trump wrote in a tweet.
It was unclear whether his remark represented a significant shift in his thinking in the US struggle to stop North Korea's nuclear programme and its test launching of missiles or a change in US policy towards China.
"I think the president is signalling some frustration, he's signalling to others that he understands this isn't working, and he's trying to defend himself, or justify himself, by saying that at least they tried as opposed to others who didn't even try," Christopher Hill, a former US ambassador to South Korea, told MSNBC.
The Trump statement about China was likely to increase pressure on Beijing ahead of a US-China Diplomatic and Security Dialogue on Wednesday.
The talks will pair US Secretary of State Rex Tillerson and Defence Secretary James Mattis with China's top diplomat, State Councilor Yang Jiechi, and General Fang Fenghui, chief of state of the People's Liberation Army.
The State Department says the dialogue will focus on ways to increase pressure on North Korea to give up its nuclear and missile programs, but also cover such areas as counter-terrorism and territorial rivalries in the strategic South China Sea.
The US side is expected to press China to co-operate on a further toughening of international sanctions on North Korea.
The United States and its allies would like to see an oil embargo and bans on the North Korean airline and guest workers among other moves, steps diplomats say have been resisted by China and Russia.
In a sign that US-Chinese relations remain stable, a White House aide said Trump's daughter Ivanka Trump and her husband, White House senior adviser Jared Kushner, were invited by the Beijing government to visit China later this year.
In a White House meeting with visiting Ukraine President Petro Poroshenko, Trump criticised the way Warmbier's case was handled in the year since his arrest, appearing to assail both North Korea and his predecessor, US President Barack Obama.
"What happened to Otto is a disgrace. And I spoke with his family. His family is incredible ... but he should have been brought home a long time ago," Trump said.
State Department spokeswoman Heather Nauert said the United States holds North Korea accountable for Warmbier's "unjust imprisonment" and urged Pyongyang to release three other Americans who are detained.
Trump's tweet about China took some advisers by surprise. A senior administration official, speaking on condition of anonymity, said the United States had limited options to rein in North Korea without Chinese assistance.
White House spokesman Sean Spicer said a meeting between Trump and North Korean leader Kim Jong Un is less likely following Warmbier's death.
Spicer said Trump would be willing to meet Kim under the right conditions, but that, "clearly we're moving further away, not closer to those conditions."