South Korea has conducted maritime research and collected samples near disputed islands, triggering a protest from Japan on Tuesday after it was brought to Tokyo's attention — a development that could further deteriorate relations between the two countries.

A paper has shown that South Korean researchers in 2012 conducted a state-funded survey in waters around the pair of islands controlled by Seoul but claimed by Tokyo, and took sediment samples from sea floor. The Japanese government alleged the activity violated the U.N. Convention on the Law of the Sea.

"If (South Korea) conducted any scientific research in Japan's territorial waters or exclusive economic zone without our prior consent, it's unacceptable," Chief Cabinet Secretary Yoshihide Suga said at a news briefing on Tuesday. "We've already lodged a strong protest."