South Korea, Japan and the United States on Monday affirmed their close cooperation in dealing with North Korea's nuclear and missile issues, at separate meetings in Seoul ahead of this week's landmark inter-Korean summit.

Kenji Kanasugi, the Japanese envoy on North Korean nuclear issues, told his South Korean counterpart Lee Do Hoon that with the rapidly developing situation on the Korean Peninsula, bilateral cooperation and three-way cooperation also involving the United States are becoming "even more important."

Lee agreed that the two countries should carry on with their consultations in a bid to "bring about significant progress" in the denuclearization of North Korea. A portion of their meeting was open to the press.

Susan Thornton, acting U.S. assistant secretary of state for East Asian and Pacific affairs, met South Korean Deputy Foreign Minister Yoon Soon Gu and told him that she is looking forward to "learning from what happens" in the inter-Korean summit on Friday, expected to be followed by the first-ever talks between the U.S. and North Korean leaders in May or June.

（Susan Thornton, left, and Yoon Soon Gu）

Thornton told reporters after their meeting that she and Yoon talked "about our good coordination" on North Korean issues and emphasized that their bilateral "cooperation is seamless."

Thornton is set to visit Japan from Tuesday.

A flurry of diplomatic activity has been taking place ahead of the summits, which are raising hopes that a breakthrough may be reached over the nuclear standoff, leading toward North Korea's denuclearization.

Speaking to reporters later in the day, Kanasugi said he welcomes North Korea's recent announcement to halt nuclear and missile tests and dismantle its main nuclear test site.

But he also said Japan and South Korea will work together to "assess and gather information" on the North's moves so that "concrete actions" will be taken toward its denuclearization, an agreement which he said was reached with Lee.

Japan has been reacting relatively cautiously to North Korea's sudden diplomatic outreach in recent months that followed repeated test-firing of missiles and underground nuclear tests, given that the North has a history of breaking promises over its nuclear and missile programs.

(Lee Do Hoon, left, and Kenji Kanasugi)