The United States has steadily blocked the pressure on China's naval forces in a way that could lower the threshold for conflict in the South China Sea, which is already a tension.
The United States signals a harder stance on the Chinese maritime militia, a paramilitary naval force disguised as a fishing fleet known to sometimes harass foreign rivals to enforce China's great sovereignty demands in the disputed waterway.
The Chinese naval military "thrives within the shadow of plausible denitability," according to Andrew Erickson, a leading expert at the US Naval War College, but it can no longer hide as it once was.
The Ministry of Defense has first referred the attention of the maritime militia in its 201
However, it was only this year that the United States really began to put pressure on the militia forces.
Chief of Naval Operations Adm. John Richardson warned his Chinese counterpart during a meeting in Beijing in January that the US Navy would treat coastguard and maritime militia vessels as campaigners and respond to provocations just like a Chinese navy ship, the Financial Times reported.
In March, Secretary of State Mike Pompeo publicly assured the Philippines that the United States would come under defense if it was attacked in the South China Sea.
"Any armed attack," he said, "on Philippine forces, aircraft or public ships in the South China Sea will trigger mutual defense obligations."
Sung Kim, the US Ambassador to the Philippines, clarified the earlier assurances on Friday and told reporters that US security guarantees apply to aggressive actions by the Chinese maritime militia.
"Any armed attack, I would think it would include government-minded militias," said the ambassador according to The Philippine Star. He did not say what kind of behavior would be an "armed attack".
The increased pressure aims to change China's strategic calculation in the disputed waterway, experts say.
"By injecting greater uncertainty about how the US will respond to China's gray zone coercion," said Bonnie Glaser, a Chinese expert at the Center for Strategic and International Studies, the Financial Times, "The United States hopes to hold Chinese destabilizing maritime behavior, including its dependence on coastguard and maritime militias to scare its smaller neighbors. "At the same time, it may make it easier for a lower conflict between China and its neighbors to escalate, especially in view of the ambiguity of both the United States' deterrent position and the role of the maritime militia.
Incidents involving Chinese fishing vessels, potential members of the maritime militia, are frequent occurrences in the South China Sea. It is unclear exactly what kind of incident can trigger US defense obligations.
In April, more than 200 Chinese fishing vessels were accused of defeating Thitu Island, a Filipino-inhabited area of the Spratly Islands.
And last week, a suspected Chinese ship was accused of ramming a Philippine ship in the South China Sea and lowering it and sailing when nearly two dozen Philippine fishermen fought for their lives in open water.
China has denied allegations of wrongdoing. And while the tensions persist, Filipino leadership has especially called for calm, suggesting that escalation is unlikely at this time.