The comments sought to address concern the United States may be rushing to strike a breakthrough in the unprecedented summit between the two leaders after US President Donald Trump put the meeting back on track for 12 June in Singapore.
"I am going to visit the DPRK and meet HE Kim Jong-un", Assad was quoted saying in the report, using the initials for North Korea's official name and referring to Kim using letters that stand for "his excellency". Yonhap named the military leaders as defense chief Pak Yong Sik, Korean People's Army chief of staff Ri Myong Su, and Kim Jong Gak, head of the KPA's General Political Bureau.
Japanese Minister of Defense Itsunori Onodera told reporters after the meeting with Mattis and South Korean Minister of National Defense Song Young-moo that the nations agreed "it is very important for North Korea to take concrete actions in a ideal and irreversible way".
Seoul has been pushing for a political declaration to end the war, possibly through a three-way summit among Moon, Trump and Kim.
Trump revived the Singapore summit on Friday after cancelling it a week earlier.
The Trump administration wants the North to "denuclearise", meaning to get rid of its nuclear arsenal, in return for relief from economic sanctions.
But North Korea's leadership is believed to regard nuclear weapons as crucial to its survival and has rejected unilaterally disarming.More news: Warriors fans cheer for J.R. Smith ahead of Game 2
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Pyongyang and Damascus maintain good relations, and United Nations monitors have accused North Korea of cooperating with Syria on chemical weapons, a charge the North denies.
Trump met with former North Korean spy chief Kim Yong Chol for about 90 minutes Friday - the highest-level North Korean official to visit the USA in 18 years.
To underscore the challenges in following North Korean affairs, the Yonhap agency reported erroneously in February 2016 that Ri Yong Gil had been executed as part of high-level purges.
All the newly promoted officials are younger than their predecessors, including 63-year-old Ri Yong-gil, who is 21 years younger than Ri Myong-su, Reuters reported.
Lower-level U.S. -North Korean talks to prepare for the summit are continuing but have made only "halting progress", according to a second U.S. official briefed on the discussions.
"North Korea will receive relief only when it demonstrates verifiable and irreversible steps to denuclearization", Mattis said during public remarks at a meeting with the South Korean and Japanese defense ministers.
"Take your time", Trump told Kim Yong Chol, a top aide to Kim.