Defense Secretary Jim Mattis is warning it will be a "bumpy road" to the nuclear negotiations with North Korea later this month. He is 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 spoke at the start of a meeting with South Korean Defense Minister Song Young-moo and Japanese Defense Minister Itsunori Onodera at the Shangri-La Dialogue security conference.

He says strengthening the allies' defense cooperation is the best path to peace.

Song says allies must be cautious, but some of Pyongyang's recent steps are reasons to be optimistic.

Plans are moving forward for a nuclear weapons summit between President Donald Trump and North Korean leader Kim Jong Un on June 12.