Research ship Onnuri / Courtesy of Korea Institute of Ocean Science and Technology

Korea and China face territorial issues as China continues to install unauthorized structures in overlapping waters in the West Sea.

According to government sources on Tuesday, Korean authorities sent a research ship on Feb. 26 to the Provisional Maritime Zone (PMZ) near Ieodo, an island off Korea's southwestern coast, to inspect a steel structure that China had installed without authorization. The ship encountered a two-hour standoff during the inspection.

Chinese coast guard ships and three rubber boats blocked the Korean vessel, Onnuri, as it approached within 1 kilometer of the structure. They claimed that it was an aquafarm and asked the Korean vessel to leave.

In response, Korea said its investigation was legitimate and dispatched a Coast Guard vessel to the scene.

Some of the Chinese civilians at the ocean structure reportedly carried knives, but no physical clashes occurred during the standoff.

The incident comes amid growing allegations that China has been installing unauthorized structures to assert its jurisdiction over disputed waters.

Last April and May, China installed several large steel structures in the PMZ zone where the Exclusive Economic Zones (EEZs) of Korea and China overlap, and added another earlier this year. It continues to insist that the installations are aquafarms.

The two countries agreed to allow their fishing vessels to operate there and jointly manage marine resources while prohibiting any activities beyond aquaculture purposes.

Korea attempted to conduct an on-site investigation on the purpose and function of the latest unauthorized structure, which was halted by China's opposition.

In response, Korea's Ministry of Foreign Affairs "delivered a firm stance" on the Chinese coast guard's threat to the Korean research vessel.

"The government has been actively responding at the pan-governmental level to ensure that our legitimate maritime rights and interests in the West Sea are not affected," the ministry said.

China's foreign ministry spokesperson Mao Ning said during a regular press conference, Tuesday, "Regarding the maritime disputes between the two sides, China and the ROK maintain sound communication through the dialogue and cooperation mechanism of maritime affairs, and the maritime law enforcement authorities of the two countries also have smooth communication channels. The situation in the [West Sea] is stable at the moment."

The Society of Ieodo Research, a Jeju-based think tank founded in 2007 that has been involved in academic research, education and promotion of the disputed underwater reef, said Wednesday that China's actions are "enough to raise suspicions and lay the groundwork for a jurisdiction claim."

Ieodo, Korea's southernmost island, also known internationally as Socotra Rock, is a subject of territorial dispute between Korea and China.

Korea has been arguing based on the "median line" principle, which means that maritime boundaries should conform to a median line equidistant from the shores of concerned countries, that the underwater reef is closer to the Korean Peninsula than to neighboring China and Japan.

However, China claims that Ieodo, which it calls Suyan, falls under its jurisdiction as the seabed topography extends from China's mainland.

"We must not get caught up in China's gray-zone tactics," the group said, referring to a range of political and military activities that occur between outright conflict and peaceful relations in international affairs.

"Korea must respond to the 'low-intensity pressure' that puts pressure on another country through non-military acts of maritime civilian or civilian fishing vessels' occupation of disputed territories," the group said.