Both South Korea and the U.S. are raising concerns over North Korea and the escalation of its military provocations under Kim Jong-un's leadership.
South Korean Defense Minister Han Min-gu has pointed to Pyongyang's third nuclear test last year and recent launches of missile and rockets as evidence of that.
He also that the North has developed more sophisticated launch methods.
And his Washington counterpart has echoed such concerns.
"There's desire for nuclear missiles and nuclear capabilities as we said over and over again are highly threatening to the global security environment."
And Locklear pointed to the strained ties between South Korean and Japan as a stumbling block in efforts to put North Korea in check and curb its nuclear weapons development.
"They have a common concern, a huge common concern with North Korea. And that we encourage them to -- both Japan and South Korea -- to work together to overcome their political difficulties so that we can work to provide a better security environment in this region."
Locklear emphasized that Seoul and Tokyo need to realize the importance of bilateral and trilateral military-to-military cooperation along with Washington.
Historical and territorial disputes between Seoul and Tokyo have dipped bilateral relations to their lowest level in years.
Connie Kim, Arirang News.