Japan has reportedly lodged a protest over South Korea's marine survey in waters off the Dokdo islets in the East Sea.

According to Japan's Kyodo News and the Sankei Shimbun daily, the Japanese foreign ministry said on Sunday that it has confirmed a South Korean research vessel conducted the survey near Dokdo.

The ministry reportedly said in a statement that the vessel was found to have extended a wire-like object into the sea waters off the islets without prior consent from Tokyo.

The Japanese ministry also said it inquired about the matter, and the South Korean government admitted to having carried out the survey.

The ministry is said to have lodged a protest with a South Korean diplomat, demanding Seoul halt the survey immediately.

It marks the first time since May 2017 that Japan has lodged a protest with South Korea over a marine survey around Dokdo. Japan claims that Dokdo is a Japanese territory, calling the islets Takeshima.