Two Chinese government vessels entered the restricted waters surrounding Itu Aba Island on June 11 — the first deliberate intrusion since Taiwan formally designated those zones in 2004.
The move shattered a cross-strait understanding that had quietly held for over two decades.
It did not happen in isolation. The Itu Aba incursion was the sharpest edge of a sustained, escalating pressure campaign Beijing launched against Japan and Taiwan between June 1 and June 12 — all triggered by a single diplomatic announcement.
On May 28, Japan and the Philippines formally agreed to begin negotiations delimiting their overlapping exclusive economic zones (EEZ) and continental shelf boundaries.
China condemned the move as a unilateral decision to open maritime boundary talks in waters east of Taiwan, accusing Tokyo and Manila of seriously infringing on Chinese territorial sovereignty and maritime rights. Taiwan's government faced a separate charge: that it was "selling out the interests of the entire Chinese nation" — apparently for welcoming the Japan-Philippines talks almost immediately after they were announced.
Those accusations became Beijing's stated justification for twelve days of coordinated pressure operations spanning the East China Sea and, ultimately, the South China Sea.
China Asserts Jurisdiction Over Yonaguni Waters for the First Time
The campaign opened with coast guard vessels. Two Chinese ships entered waters southeast of Taiwan on June 1, then moved deliberately into Japan's EEZ south of Yonaguni Island, where they lingered until June 8.
When Japan's coast guard contacted them by radio to ask their intentions, the response was unambiguous: "This is Chinese jurisdictional waters. We are conducting routine patrols."
It was the first time Beijing had explicitly claimed authority over those waters.
A second maritime column followed. China's Ministry of Transport, operating jointly with the Fujian Maritime Safety Administration and three other agencies, deployed a four-vessel task group from June 6 to 10. The flotilla was led by the 10,000-tonne patrol ship Haixun 09, operating under the banner of a "special maritime traffic law enforcement operation."
After transiting Taiwan's eastern waters, the group entered the western Pacific, moved north along Taiwan's eastern coastline, passed deliberately through waters near Yonaguni, and then proceeded toward the Diaoyutai/Senkaku Islands.
The choice of Yonaguni was not incidental. As Japan's westernmost inhabited island, it sits near the overlapping EEZ waters at the heart of the Japan-Philippines dispute. By asserting jurisdictional claims there, Beijing extended its maritime enforcement posture beyond the East China Sea into Japan's southwestern periphery — territory it had not previously targeted so explicitly.
It marks a clear escalation of China's grey-zone playbook against Japan.
Yonaguni Sits 110 km From Taiwan With Missiles Planned by 2030
The island carries strategic weight that amplifies its symbolic role.
Yonaguni lies just 110 kilometers from Taiwan. Japan has already deployed a coastal surveillance unit and mobile radar station on the island, and Tokyo plans to station Type-03 medium-range surface-to-air missiles there by 2030.
In peacetime, those capabilities allow Japan to monitor People's Liberation Army (PLA) activity around the Taiwan Strait. In a conflict scenario, Yonaguni would serve as a front-line expeditionary base for U.S. and Japanese forces seeking to slow PLA naval and air assets from breaking into the western Pacific.
Beijing has long been uneasy with Japan's military build-up on the island. That discomfort hardened when Prime Minister Sanae Takaichi said in the Japanese Diet last year that a serious armed conflict involving China — particularly over Taiwan — could constitute an existential threat to Japan.
Beijing read the remark as encouragement for what it characterizes as Taiwan's pursuit of independence through external alignment.
When Taiwan's Ministry of Foreign Affairs publicly welcomed the Japan-Philippines boundary talks shortly after May 28, Beijing appears to have interpreted that endorsement as evidence that Taipei was prepared to trade maritime jurisdiction concessions for diplomatic and security support from Tokyo and Manila.
Beijing's pressure on Yonaguni therefore carried a dual message. It established a precedent for Chinese law enforcement operations near Taiwan's eastern EEZ, bolstering its legal warfare claims in that area. And it sent Tokyo a direct warning: any further moves construed as supporting Taiwan's international position would carry a cost.
The PLA Mounted Three Consecutive Operations Targeting Okinawa and the Senkakus
Beijing did not confine its response to coast guard vessels. Starting June 6 — the same day the maritime law enforcement flotilla departed — the PLA conducted three separate pressure operations directed at Okinawa and the Diaoyutai/Senkaku Islands.
The first involved two Eastern Theater Command Navy warships: the Type 052D destroyer Nanjing and the Type 054A frigate Binzhou. The pair arrived in the contiguous zone south of Okinawa's main island on June 6, then moved slowly northward along its eastern coast, rounding Amami Oshima and Kikaijima before returning westward into the East China Sea on June 10.
On June 9, the ships were operating roughly 20 nautical miles from Kikaijima's eastern contiguous zone — at the same moment the maritime law enforcement flotilla was transiting Yonaguni. Together, they created a coordinated east-west encirclement posture around Okinawa.
The second wave came on June 11. Between 7:50 a.m. and 8:40 p.m., seven PLA aircraft sorties departed from airspace north of Dongyin Island, crossed the Taiwan Strait median line, and flew eastward — remaining south of the 27th parallel — to approximately 123 degrees east longitude. Their heading pointed toward the northern airspace above the Diaoyutai/Senkaku Islands. At their closest point on the return leg, the aircraft were reportedly about 102 kilometers from the islands.
The third operation came on June 12. A Y-9 electronic reconnaissance aircraft and a TB-001 multi-role unmanned aerial vehicle flew into the East China Sea, tracked southwest toward waters south of Nagasaki Prefecture's Danjo Islands, then turned westward near the outer waters off Okinawa. At their nearest, the aircraft were approximately 166 kilometers from the Diaoyutai/Senkaku Islands.
The conventional military utility of all three operations was limited. Their purpose was demonstrative: to signal Tokyo that further moves seen as facilitating Taiwan's international position would meet a sustained and escalating response.
An Itu Aba Intrusion Revives a Decade-Old Beijing Fear
The most consequential move in the entire sequence came on June 11.
Two large vessels identified as belonging to the Sansha Comprehensive Law Enforcement Detachment — displacing 8,000 and 4,800 tonnes respectively — deliberately entered the restricted waters surrounding Itu Aba Island (Taiping Island, 太平島), Taiwan's sole outpost in the South China Sea. The ships came within 2.1 nautical miles of the island at their closest point.
Itu Aba lies more than 1,400 kilometers from the EEZ overlap at the center of the Japan-Philippines dispute.
It was the first such deliberate intrusion since Taiwan formally gazetted Itu Aba's restricted and prohibited waters on June 7, 2004. A tacit cross-strait understanding that had preserved those boundaries for 22 years was broken in a single operation.
The most plausible explanation connects back to Taiwan's prompt public endorsement of the Japan-Philippines boundary talks. In Beijing's reading, that statement signaled that Taipei might be willing to trade away maritime claims in exchange for diplomatic backing from Japan, the Philippines, and the United States — what Beijing frames as pursuing de facto independence through external alignment.
That reading appears to have reactivated a long-standing fear in Beijing: that a DPP-led government might eventually adjust Taiwan's South China Sea sovereignty claims, just as it may now be doing in Taiwan's eastern EEZ.
This anxiety has a documented history. When the Philippines filed its South China Sea arbitration case at the International Tribunal for the Law of the Sea in 2013, Washington urged the Ma Ying-jeou (馬英九) administration — publicly and privately — to reconsider or "clarify" the Republic of China's South China Sea claims. Beijing's concern deepened through 2015 as it became clear that Tsai Ing-wen (蔡英文) would likely win the 2016 presidential election.
After Tsai's January 2016 victory was confirmed, Beijing issued direct warnings. Shi Yinhong (時殷弘), then a State Council counselor and director of Renmin University's American Studies Center, said publicly that Beijing's concern was whether the new government would help the United States and Southeast Asian nations undermine China's South China Sea sovereignty — including by abandoning the Republic of China's historic eleven-dash line claim.
"Abandoning the South China Sea claim could be seen as connected to formal independence," he said. "Beijing's reaction would be very strong."
Guo Xiankang (郭憲綱), then deputy director of the China Institute of International Studies under the Foreign Ministry, was equally direct: "If the eleven-dash line is abandoned in the hope of weakening the connection between Taiwan and the mainland, that can certainly be characterized as indirect pursuit of Taiwan independence."
Those fears were ultimately defused when the Tsai government's response to the July 2016 arbitration ruling did not abandon the eleven-dash line. But the June 11 intrusion at Itu Aba suggests the underlying anxiety has resurfaced — reactivated by the Japan-Philippines talks and Taiwan's immediate endorsement of them.
Normalizing Patrols Around Itu Aba Could Trigger a Regional Cascade
Breaking the 22-year understanding around Itu Aba served Beijing as both a deterrent signal to Taipei and a possible opening move toward regularizing Chinese law enforcement patrols in those restricted waters.
If China does normalize such patrols, the consequences would not be confined to cross-strait relations.
Vietnamese and Philippine coast guard operations in the same waters would likely intensify in response, producing a significant deterioration in the security environment around Itu Aba.
Taiwan's national security agencies should begin contingency planning for that scenario now, before it materializes.
*The author is an associate research fellow at the Division of Defense Strategy and Resources, Institute for National Defense and Security Research. （Related： Taiwan Toughens Reserve Call-Ups: 56 Days, Women Next ｜ Latest ）
