"We are strongly concerned about dangerous conduct and intimidation by vessels in the disputed area," she told a regular news briefing.

"We call on all parties to conduct themselves in a safe and appropriate manner, exercise restraint, and address competing sovereignty claims peacefully, diplomatically, and in accordance with international law."

Psaki said the United States had seen reports that Philippine police had seized Chinese and Philippine fishing boats carrying illegally harvested sea turtles in the East Sea and detained their crews.

"We urge both sides to work together diplomatically," she said. "Given the United States works with the international community to combat wildlife trafficking, we are concerned that the vessels appear to be engaged in direct harvest of endangered species of sea turtles."

China has demanded that the Philippines release its boat and fishermen.