In this June 12, 2018, photo, U.S. President Donald Trump stands with North Korean leader Kim Jong-un during a meeting on Sentosa Island, Singapore. For some observers, the nightmare result of the second summit between Trump and Kim is an ill-considered deal that allows North Korea to get everything it wants while giving up very little, even as the mercurial leaders trumpet a blockbuster nuclear success. AP

North Korea warned U.S. President Donald Trump on Sunday not to listen to U.S. critics who weredisrupting efforts to improve ties, as its leader, Kim Jong-un, made his way across China by train to a second summit with Trump in Vietnam.

The two leaders will meet in Hanoi on Wednesday and Thursday, eight months after their historic summit in Singapore, the first between a sitting U.S. president and a North Korean leader, where they pledged to work toward the complete denuclearisation of the Korean peninsula.

But their vaguely worded agreement has produced few results and U.S. Democratic senators and U.S. security officials have warned Trump against cutting a deal that would do little to curb North Korea's nuclear ambitions.

The North's KCNA state news agency said such opposition was aimed at derailing the talks.

"If the present U.S. administration reads others' faces, lending an ear to others, it may face the shattered dream of the improvement of the relations with the DPRK and world peace and miss the rare historic opportunity," the news agency said in a commentary, referring to North Korea by the initials of its official name, the Democratic People's Republic of Korea.

The Trump administration has pressed the North to give up its nuclear weapons programme, which, combined with its missile capabilities, pose a threat to the United States, before it can expect any concessions.

But in recent days Trump has signalled a possible softening, saying he would love to be able to remove sanctions if there is meaningful progress on denuclearisation.

Trump also said he was in no rush and had no pressing schedule for North Korea's denuclearisation, hinting at a more gradual, reciprocal approach, long favoured by Pyongyang.

The North also wants security guarantees and a formal end of the 1950-1953 Korean War, which ended in a truce, not a treaty.

Trump said on Sunday that he and Kim expect to make further progress at this week's summit and again held out the promise that denuclearization would help North Korea develop its economy.

He also said Chinese President Xi Jinping has been supportive of Trump's meeting with Kim. "The last thing China wants are large scale nuclear weapons right next door."

TRUMP SCOFFS AT CRITICS

Trump scoffed at critics of his handling of North Korea.

"So funny to watch people who have failed for years, they got NOTHING, telling me how to negotiate with North Korea. But thanks anyway!" he said in a tweet.