Kuala Lumpur summoned China’s ambassador to Malaysia on Monday to protest a recent violation of its South China Sea maritime territory by Chinese vessels off the coast of Borneo.

Malaysia’s Foreign Ministry requested a meeting with Chinese Ambassador to Malaysia Ouyang Yujing on October 4 to convey the nation’s objection to a recent incursion of Chinese vessels, “including a survey vessel,” near the Malaysian states of Sabah and Sarawak, which are located on northern Borneo Island. Kuala Lumpur did not provide a date for the alleged incident.

“The Ministry of Foreign Affairs today called in the Ambassador of the People’s Republic of China to convey Malaysia’s position and protest against the presence and activities of Chinese vessels, including a survey vessel, in Malaysia’s Exclusive Economic Zone off the coasts of Sabah and Sarawak,” Malaysia’s Foreign Ministry confirmed in a press release issued October 4.

“The presence and activities of these vessels are inconsistent with Malaysia’s Exclusive Economic Zone Act 1984, as well as the 1982 United Nations Convention on the Law of the Sea (UNCLOS),” the ministry noted.

Borneo is the largest island in Asia and the third-largest in the world. It is politically divided between Malaysia, Brunei, and Indonesia. The island is located at the heart of maritime Southeast Asia. Its geographic splintering represents a microcosm of the often overlapping territorial claims within the hotly disputed South China Sea, which Beijing claims almost in its entirety. The South China Sea is highly coveted by China for its strategic shipping lanes and untapped oil and natural gas deposits.

Malaysia last summoned its Chinese ambassador in June to protest another alleged violation of its sovereignty near Borneo.

According to a press release issued by the Royal Malaysian Air Force (RMAF) on June 1, “16 Xi’an Y-20 and Ilyushin Il-76 airlifters of the People’s Liberation Army Air Force, or PLAAF, approached to within 60 nautical miles (69 miles) of Malaysia’s coast.”

The Chinese aircraft approached Malaysian Borneo in a “tactical formation” and were first detected by an RMAF radar system above Sarawak state on the morning of May 31. The PLAAF detachment flew “at 290 knots in a southwesterly direction in neighboring Singapore’s flight information region before turning to the south and crossing into international airspace administered by Malaysian air traffic control, operating at altitudes between 23,000 and 27,000 feet,” according to the RMAF.

Defense News reported at the time:

[The Chinese planes] failed to respond to several attempts by Malaysian air traffic controllers to contact them, after which the RMAF scrambled BAE Systems-made Hawk 208 light combat jets from nearby Labuan airbase at 1:33 p.m. after the ‘suspicious aircraft’ were first sighted, to intercept and identify them.

Malaysia accused China of breaching its sovereignty with the air incursion, while Beijing maintained the activity was part of routine training by the PLAAF.