Kim Jong Un's regime conducted an unprecedented seven weapons tests in January, including launching its most powerful missile since 2017 as it hinted it could restart long-range and nuclear testing.

Washington had proposed a statement decrying those launches, but China and Russia, along with other nations, refused to sign on to it, the diplomats told AFP.

"If they do want to see some new breakthrough, they should show more sincerity and flexibility," China's ambassador to the UN, Zhang Jun, said of US officials ahead of a closed-door meeting convened at Washington's request on North Korea.

"They should come up with more attractive and more practical, more flexible approaches, policies and actions and accommodating the concerns of the DPRK," Zhang told reporters, using the initials of the North's official name.

The Chinese official noted that as a result of former US president Donald Trump's policy on North Korea, Pyongyang had suspended nuclear tests and international ballistic missile launches.

However, in recent months, Zhang lamented, "we have seen a vicious circle of confrontation, condemnation, sanctions."

China and Russia have been blocking UN Security Council action on North Korea, and last year called for easing sanctions on Pyongyang on humanitarian grounds.

"At least we are doing something to facilitate further improvement and avoiding the escalation of the tension," Zhang said.

North Korea on Friday sent "warm congratulations" to its Chinese ally for the Beijing Olympics, a message that experts consider a likely signal for a halt to missile firing during the sporting event.

US Secretary of State Antony Blinken is scheduled to hold trilateral talks in Hawaii on February 12 with South Korea and Japan on North Korea.