(CNN) Two top Trump administration officials insisted Wednesday that the United States and China share a common understanding about the threat posed by North Korea, one day after President Donald Trump tweeted that a Chinese attempt to bring the regime in line "has not worked out."
"China understands that the United States regards North Korea as our top security threat," Secretary of State Rex Tillerson told reporters following meetings with Chinese counterparts. "We reiterated to China that they have a diplomatic responsibility to exert much greater economic and diplomatic pressure on the regime if they want to prevent further escalation in the region."
Secretary of Defense James Mattis reinforced the message, calling the dialogue "open and frank," and insisting, "China continues to work these issues."
For months, the Trump administration has lobbied China to exert its economic influence over the North Korean government in an effort to halt that country's nuclear weapons and missile development activities.
But in a tweet Tuesday, Trump suggested those efforts had failed.
"While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out," Trump wrote. "At least I know China tried!"
Asked about President Trump's tweet, Mattis said, "I believe he represents the American people's view of North Korea right now."
Trump said Wednesday at a rally in Cedar Rapids, Iowa that US has "a very good relationship with China and I do like President Xi." However he added: "I wish we would have a little more help with respect to North Korea from China but that doesn't seem to be working out."
Speaking to reporters Thursday, Chinese Foreign Ministry spokesman Geng Shuang said that Beijing "does not exert so-called economic or diplomatic pressures" on other countries.
"On the North Korea nuclear issue, I'd like to reiterate that China has been making persistent efforts to promote a resolution to the issue," he said. "As we have repeatedly said, the root cause to the North Korea issue is not China. The key to a resolution isn't in China's hands, either. We hope to see the relevant parties shoulder their own responsibilities, play their proper roles and work with China to resolve the issue."
Referring specifically to the case of Otto Warmbier -- a 22-year-old American college student who died Monday after being released from North Korean captivity in a vegetative state -- Mattis said, "there's no way that we can look at a situation like this with any kind of understanding."
"This goes beyond any kind of understanding of law and order, of humanity, of responsibility towards any human being," he added.
Tillerson and Mattis spent most of Wednesday in closed-door meetings with Chinese State Councilor Yang Jiechi and General Fang Fenghui of the People's Liberation Army Joint Staff, with the aim of building on diplomatic momentum from the April meeting between Trump and President Xi Jinping in Mar-a-Lago.
Tillerson said the delegations also had a "frank exchange of views on the South China Sea," where the Chinese military is engaged in a controversial island-building project, which the United States opposes.