Philippine fishing authorities said Tuesday they had detained 25 Chinese crew of two seized fishing boats on suspicion of poaching, a move that could further strain ties between two countries at odds over maritime sovereignty.

A joint team from the Philippine coast guard and the Bureau of Fisheries and Aquatic Resources (BFAR) captured the Chinese vessels Monday sailing without permits between waters off Babuyan Island and Batanes province in the northern Philippines.

The Chinese vessels were in waters that are not part of the disputed South China Sea, which China claims almost entirely. Brunei, Malaysia, the Philippines, Vietnam and Taiwan also have conflicting claims.