Secretary of State Rex Tillerson called for nations to step up the US-led "maximum pressure" campaign against North Korea by thwarting sanctions evasion and interdicting ships conducting illicit trade with the pariah nation.
Foreign Affairs Minister Winston Peters left for Canada on Monday to attend the international meetings on North Korea.
Mr Peters said the "meeting is also an opportunity for the international community to demonstrate solidarity in opposition to the North Korean nuclear tests and missile launches".
"We want North Korea to understand the importance which the international community places on it returning to a meaningful dialogue on denuclearisation," he said.
The meeting is being attended by foreign ministers and senior diplomats of nations that sent troops or humanitarian aid to the UN Command that supported South Korea in the fight against the communist North and its allies during the 1950-53 Korean War.
It's a diverse gathering of mostly European and Asian nations, as well as Australia, New Zealand and Columbia. Officials are discussing sanctions, preventing the spread of weapons by North Korea, and diplomacy.
The gathering, co-hosted by Canada and the US, is strongly opposed by China and Russia, which fought on the communist side in the war. It appears primarily symbolic and unlikely to break much new ground.
Mr Tillerson's uncompromising message delivered to a gathering of 20 nations that were on America's side during the Korean War came despite the recent diplomatic opening between the rival Koreas after a year of escalating tension.
"We must increase the costs of the regime's behavior to the point that North Korea must come to the table for credible negotiations," Tillerson said in his opening remarks at the meeting on Canada's western coast. The meeting convened days after a mistaken missile alert caused panic on Hawaii, a stark reminder of the fears of conflict with the North.
South Korean Foreign Minister Kang Kyung-wha said its talks with North Korea, leading to its participation in next month's Olympics being hosted by the South, are a "significant first step toward restoring inter-Korean relations."
But she conceded that despite the overtures, North Korea has yet to show any intention to fulfill its obligations on denuclearization of the Korean Peninsula.
Japanese Foreign Minister Taro Kono was blunter. He said the North "wants to buy some time to continue their nuclear and missile programmes."
Although Mr Tillerson said the meeting sends North Korean leader Kim Jong Un a unified message that a nuclear-armed North is unacceptable, it risks alienating Beijing and Moscow.
They are Pyongyang's main trading and diplomatic partners, but have nevertheless supported UN Security Council resolutions to restrict revenue for North Korean nuclear and missile development.