TAIPEI (Taiwan News) — The Philippines on Tuesday challenged a Chinese research vessel off its northern coast as China carried out large-scale military exercises around Taiwan.

Reuters reported Wednesday that the Philippine Coast Guard sent an aircraft to confront the Chinese ship after it was spotted about 19 nautical miles (35.19 km) off Cagayan province in northern Luzon. The area sits close to Taiwan and falls within the Philippines’ exclusive economic zone.

The coast guard said the vessel, identified as Tan Suo Er Hao, may have been conducting marine research without Philippine approval, which would violate domestic and international rules. It added that repeated radio calls were made, but no reply was received.

The Manila Bulletin reported Wednesday that the ship later sailed east and was monitored about 55.8 nautical miles off Santa Ana, Cagayan. The coast guard said it tracked the vessel using Canada’s Dark Vessel Detection satellite system.

Cagayan is the Philippines’ northernmost province and hosts one of the military bases open to US forces under the Enhanced Defense Cooperation Agreement. Philippine officials have said the province’s location makes it sensitive to developments around Taiwan.

China’s embassy in Manila said the ship was on routine operations and insisted China has the right to pass through the waters under international law, according to Reuters. It also said Beijing does not accept some Philippine maritime laws.

The incident came as China staged major military drills around Taiwan, firing rockets and simulating blockades in exercises called “Justice Mission 2025.” The drills followed a US announcement of an US$11.1 billion (NT$348 billion) arms package for Taipei.

Philippine Defense Secretary Gilberto Teodoro said Manila was “deeply concerned” about China’s military and coast guard actions linked to Taiwan, per Reuters. He said the moves could undermine regional peace and affect not just cross-strait ties but the wider Indo-Pacific.