Japan will effectively lower South Korea's standing as an important security cooperation partner in this year's defense white paper, a Defense Ministry source has said, reflecting the worsening of bilateral ties.

In a chapter dedicated to Japan's security cooperation with countries other than its closest ally, the United States, South Korea came second in 2018. But its place has fallen to fourth this year after Australia, India and the Association of Southeast Asian Nations (ASEAN), according to a draft of the 2019 defense white paper.

"In effect, (the order) means a downgrade" for South Korea, the ministry source said Friday. The white paper is expected to be made public around mid-September.