U.S. Secretary of State Mike Pompeo, right, attends a joint news conference with South Korean Foreign Minister Kang Kyung-wha, center, and Japanese Foreign Minister Taro Kono, left, following their meeting at Foreign Ministry in Seoul, South Korea, Thursday. AP-Yonhap

U.S. Secretary of State Mike Pompeo said Thursday his administration has not dropped the aim of denuclearizing North Korea in a "complete, verifiable and irreversible" manner, apparently in response to criticism about the Singapore summit deal.

Speaking after talks with his South Korean and Japanese counterparts here, he stressed that there would be no sanctions relief for Pyongyang before that.

The United States and the two other regional powers remain "committed to the complete, verifiable and irreversible denuclearization (CVID) of North Korea," he said at a joint press conference.

His remarks came as some media and experts find fault with President Donald Trump's Singapore summit accord with the North's leader Kim Jong-un, which has no clear mention of Washington's stated goal of CVID.

The accord just stipulates that the communist nation will "work towards complete denuclearization of the Korean Peninsula." The two sides agreed to establish "new relations" to end seven decades of hostility dating back to the 1950-53 Korean War.

Trump said he had skipped the CVID jargon in the joint statement due to time constraints and Pompeo told reporters the word "complete" encompasses the notion of verification.

Pompeo, a former CIA director, said Kim appears to understand the need for a quick process.

"We believe that Chairman Kim Jong-un understands the urgency of the timing of completing this denuclearization and understands we must do this quickly," he said, "And the sanctions relief cannot take place until such time as we have demonstrated that North Korea has been completely denuclearized."

The summit deal, he added, will be implemented on a "sequencing, conditions" basis "with eyes open."

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U.S. Secretary of State Mike Pompeo looks on as he attends a bilateral meeting with South Korea's President Moon Jae-in at Cheong Wa Dae in Seoul, June 14. REUTERS-Yonhap

He emphasized that trilateral cooperation among the three regional powers is "crucial to the effectiveness" of the process, which is "not an easy one."

South Korea's top diplomat, Kang Kyung-hwa, described the Singapore event, an unprecedented bilateral summit between the Korean War war foes, as a "historic turning point," saying it marks the first time that the "highest authorities of the North Korea promised to a 'sitting' U.S. president to work towards complete denuclearization."

Kang dismissed concerns about a possible crack in the Seoul-Washington alliance over Pyongyang.

It's "as robust as ever" and the South expects "no daylight" in cooperation with the U.S. towards the denuclearization of the peninsula and peace.

On Trump's talk of suspending major combined military drills between the allies, which he calls "expensive and provocative war games," the minister said it's an issue to be decided through consultations between their defense authorities.

Keen attention is being paid to whether they will stage the Ulchi Freedom Guardian (UFG) joint exercise in August as scheduled.

Japan's Foreign Minister Taro Kono said the U.S. Forces Korea should continue to play a key role in regional deterrence and stability.

Ahead of the trilateral meeting, meanwhile, Pompeo paid a courtesy call on President Moon Jae-in, who is credited with having played a key role in creating the current dialogue mood.

"I think what's tremendously valuable is that (the Singapore summit) has made people of the world, including those in the U.S., Japan and Korea, escape the threat of war, nuclear weapons and long-range missiles," Moon was quoted as telling Pompeo.

The top U.S. diplomat is scheduled to visit Beijing later in the day for talks with Chinese Foreign Minister Wang Yi. (Yonhap)