Japan has lodged a protest via diplomatic channels with South Korea after Seoul reportedly proposed to install military units on certain islets which are contested by the two countries in the Sea of Japan, also called the East Sea.

The two countries, both of them close allies of the US, have been engaged in territorial disputes over islets located in the region for a while now, with a pair of rocky islets – known as Dokdo in South Korea and Takeshima in Japan – at the centre of the dispute.

The islets are located roughly 210km from South Korea and 25km from Japan.

"We cannot totally accept (the plan). We strongly protested it," Japan's Foreign Minister Taro Kono told reporters on Friday, 20 October, regarding Seoul's proposals. "Under the current security situation, Japan, the United States and South Korea have to strengthen ties in a future-oriented manner. [This decision] runs counter to that."

The Japanese minister explained that this is a vital phase for close cooperation between Japan and South Korea, with both countries facing severe threats from rogue neighbour North Korea as Pyongyang makes aggressive military moves.

His comments come a day after media reports surfaced saying Seoul is planning to set up military installations on those disputed islands between 2018 and 2020 in order to defend the "strategic islands".

The rocky islets were returned to South Korea after Japanese colonial rule ended in 1945 in the Korean Peninsula. However, Japan's recent territorial claims over the islets have raised concerns in South Korea, with Seoul deploying a posse of police personnel in them.