HONG KONG — Raising the stakes in its confrontation with China, the Philippines said Saturday that it had imprisoned 11 Chinese fishermen who were caught with endangered sea turtles in a part of the South China Sea that is claimed by both nations.

The fishermen were seized on Tuesday by the Philippine National Police, who found the 350 marine turtles after intercepting the fishing boat off Half Moon Shoal in the Spratly Islands.

The run-in has been overshadowed by a clash between Chinese and Vietnamese ships 120 nautical miles off the coast of Vietnam, where China has been setting up an oil rig in waters claimed by both nations. In that case, Chinese ships fired water cannons at Vietnamese Sea Guard ships that had confronted the Chinese vessels, and both countries say the other’s ships rammed theirs.

The fishermen who were detained by the Philippines face prison terms ranging from 12 to 20 years. They are being held on charges of violating wildlife protection laws.