Japan will effectively lower South Korea's standing as an important security cooperation partner in this year's white paper on defense, a Defense Ministry source said Friday, 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, according to a draft white paper on defense for 2019.

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

The draft document urges Seoul to address Tokyo's concerns "properly," citing recent incidents, including one in December in which a South Korean destroyer allegedly locked its fire-control radar on a Japanese Self-Defense Force plane in Japan's exclusive economic zone.

In the 2018 white paper, the Defense Ministry acknowledged that the two countries have "difficult bilateral issues" but added it is important to advance relations "in a future-oriented manner."

Bilateral ties have deteriorated sharply since last year due to a series of court rulings in South Korea that ordered Japanese firms to pay damages for wartime labor during Japan's 1910-1945 colonization of the Korean Peninsula. The two nations are also in a dispute over trade.

Prime Minister Shinzo Abe, who has shunned holding a summit with South Korean President Moon Jae In ever since the rulings, has said a lack of mutual trust is the biggest issue confronting the bilateral relationship as Tokyo maintains that the compensation issue was settled under a 1965 bilateral accord.

The disputes have also moved into the military realm, with South Korea now threatening to consider ending a military intelligence-sharing pact with Japan as the end-of-August deadline for deciding whether to renew it is fast approaching.

Signed in 2016, the General Security of Military Information Agreement is seen as vital for Japan and South Korea to jointly cope with threats from North Korea's missile and nuclear development.

Meanwhile, the draft white paper also says that Japan will work with South Korea in addressing the situation in North Korea, saying it poses a "serious and imminent threat," the same expression used in 2018.

Pyongyang's repeated firing of short-range ballistic missiles has left its neighbors on alert.