The absence of Russia and China from the two days of talks in Vancouver, which began on Monday, shows the holes in Washington's bid to form a unified global front against North Korea's nuclear threat.
"The most important relevant parties of the Korean peninsula issue haven't taken part in the meeting so I don't think the meeting is legal or representative," Chinese foreign ministry spokesman Lu Kang told a regular briefing.
Lu denounced the "Cold War mentality" of "relevant parties" -- without naming nations.
China, which is North Korea's main economic and diplomatic ally, has criticised the Vancouver talks and called for sanctions discussions to remain within the United Nations framework.
While Russia and China have backed UN sanctions against North Korea, they have pushed for the United States to halt military drills in the region in return for Pyongyang suspending weapons tests.
Steve Goldstein, a senior US State Department official, told reporters last week that China and Russia were not invited to the meeting but would be briefed about it "right when it is over".
The US, which at the summit will review with its allies the effectiveness of current sanctions against the hermit kingdom and explore adding more, remains sceptical that leader Kim Jong-Un is ready to negotiate away his weapons programme.
The so-called Vancouver Group is formed by 20 countries that fought in the 1950-53 Korean War. They include Australia, Britain, France, India, Japan, the Philippines and South Korea. Military officials will also be present at the meeting.
Russian Foreign Minister Sergei Lavrov slammed the US on Monday, saying: "Unfortunately, our American colleagues and their allies still want to do business solely on the basis of issuing ultimatums and do not want to listen to the views of other centres of world politics."
Xi, Trump talk
Tensions have been high after the North staged a flurry of nuclear and missile tests.
Over the weekend, a false alarm in Hawaii warning of an incoming ballistic missile rattled nerves, while US President Donald Trump has traded bluster with Kim over who has the bigger nuclear launch button at his desk.
Trump has pushed Chinese leader Xi Jinping to increase economic and political pressure on North Korea in the hopes of convincing it to stop the development of its nuclear weapons programme.
But in recent weeks there has been an apparent rapprochement, with the two Koreas meeting for the first time in two years and Pyongyang agreeing to send athletes to the Pyeongchang Winter Olympics in South Korea.
In a phone call with Trump, Xi "pointed out that the situation on the Korean peninsula has shown some positive changes," the official Xinhua news service said Tuesday.
"All sides concerned should make joint efforts to keep up the hard-won momentum for the easing of the situation on the Korean peninsula and create conditions to restart talks," he was quoted as saying.
He also urged Trump, who has taken a hard line against the trade imbalance between China and the US, to come to the table on economic issues.
"The two countries should adopt constructive means to properly settle economic and trade issue of mutual concern through opening up markets to each other and making the cake of cooperation bigger," Xinhua quoted Xi as saying
