In comments clearly directed at the U.S. and North Korea, Liu said instead of complying with Security Council calls to de-escalate tensions and re-launch six-party negotiations, tensions have heightened as a result of new missile tests, statements that "all options are on the table," and deployment of the U.S. THAAD anti-missile system.
And in criticism aimed specifically at the United States, the Chinese ambassador said implementation of Security Council resolutions is also being hampered by unilateral sanctions and "preconditions put to starting the dialogue" with Pyongyang.
The Trump administration has declared that all options, including a targeted military strike, are on the table to block North Korea from carrying out threats against the United States and its allies in the region. But a pre-emptive attack isn't likely, U.S. officials have said, and the administration has been pursuing a strategy of pressuring Pyongyang through new unilateral sanctions and appealing to China to use its influence.
Pyongyang's two recent successful tests of intercontinental ballistic missiles have created even more urgency as the U.S. administration seeks to stop its efforts to master the complex process of mounting a nuclear warhead capable of hitting the United States.
As for resuming talks, which stalled in 2009, the United States has said it won't enter negotiations with North Korea until the country proves it will move toward abandoning its nuclear weapons program.
Trump tweeted Sunday: "We will no longer allow this to continue. China could easily solve this problem!" And U.S. Ambassador to the United Nations Nikki Haley joined in the criticism, saying China "must decide whether it is finally willing to take this vital step" of getting tough on the North.
Liu, at a news conference marking the end of China's presidency of the Security Council in July, tried to shift the responsibility for engaging North Korea from Beijing to Washington and Pyongyang.
"They hold the primary responsibility ... to start moving in the right direction, not China," he said.
"China has been implementing the (U.N.) resolutions in good faith, in the comprehensive way," Liu said, "and we urge other countries to do so. The fact that the resolutions are not so far implemented in the comprehensive and precise way says a lot about the kind of difficulties that we face at the moment."
He said the international community should move together on several fronts "make sure that the political will to resolve the issue of denuclearization is translated into actual moves, negotiations, dialogue, reducing tension on the ground," and ensure that there is no international support for North Korea's nuclear and ballistic missile programs.
Liu said China will keep working with other countries to achieve denuclearization and peace and stability on the Korean Peninsula, and "we believe that each relevant party should ... shoulder the responsibility, and uphold the obligations provided for in the relevant Security Council resolutions."
He said China is still seeking support for its proposal in which North Korea would suspend nuclear and missile tests in exchange for the U.S. and South Korea halting their joint military exercises. The package proposed by China and backed by Russia also includes denuclearization of the Korean Peninsula and "a peace and security mechanism" in place for both North Korea and South Korea, Liu said.
The Security Council has already imposed six rounds of progressively tougher sanctions against North Korea, and the United States is discussing a new sanctions resolution with China.
Liu said he is in contact with ambassador Haley "on a daily basis" and the new resolution is "under discussion."
Following the two recent missile tests, he said, it's important to look at how to eliminate nuclear weapons and ensure peace on the Korea Peninsula and "what measures should be put in place to prevent further testing, and at least to make sure that the nonproliferation regime works better to stop the nuclear and ballistic missile programs."