Mattis says he's predicting a 'bumpy road' to nuclear negotiations with North Korea this month - and that allies must stay vigilant

Associated Press/Yong Teck Lim

From left, South Korea's National Defense Minister Song Young-moo, U.S. Defense Secretary Jim Mattis and Japan's Defense Minister Itsunori Onodera shake hands before their trilateral meeting at the 17th International Institute for Strategic Studies (IISS) Shangri-la Dialogue, an annual defense and security forum in Asia, in Singapore, Sunday, June 3, 2018.

• US Defense Secretary Jim Mattis warned Sunday that there will be a "bumpy road" ahead of the nuclear summit between the US and North Korea in June.
• Plans are moving forward for a summit between President Donald Trump and North Korean leader Kim Jong Un on June 12 in Singapore.
• Mattis told his South Korean and Japanese counterparts at a conference that they must maintain a strong, defensive stance.

It will be a "bumpy road" to the nuclear negotiations with North Korea later this month, Defense Secretary Jim Mattis warned Sunday in Singapore, telling his South Korean and Japanese counterparts they must maintain a strong defensive stance so the diplomats can negotiate from a position of strength.

Mattis was speaking at the start of a meeting with South Korean Defense Minister Song Young-moo and Japanese Defense Minister Itsunori Onodera on the final day of the Shangri-La Dialogue security conference. He said allies must remain vigilant.

"We can anticipate, at best, a bumpy road to the negotiations," Mattis said. "In this moment we are steadfastly committed to strengthening even further our defense cooperation as the best means for preserving the peace."

Plans are moving forward for a nuclear weapons summit between President Donald Trump and North Korean leader Kim Jong Un on June 12 in Singapore. And Mattis repeated the US position that North Korea will only receive relief from UN national security sanctions when it demonstrates "verifiable and irreversible steps" to denuclearization.

Through an interpreter, Song said that this is a great turning point as North Korea takes its first steps toward denuclearization.

"Of course, given North Korea's past, we must be cautious in approaching this," he added that some of North Korea's recent measures "give us reasons to be positive and one can be cautiously optimistic as we move forward."

One of those measures included North Korea's recent claim to have destroyed its Punggye-ri nuclear test site - which American journalists were permitted to witness.

The demolition appeared to be a major concession from Pyongyang and a step toward the US demand for total denuclearization, and it was intended to show that the Hermit Kingdom is taking its negotiations with the US seriously.

But some of the journalists who attended the demolition said they were skeptical - and that since no nuclear experts were permitted to attend, it was difficult for them to discern whether the site's destruction was authentic or superficial.

John Haltiwanger contributed reporting.