A little noticed organizational change in China's maritime patrols is causing increasing anxiety among Western military officials and their allies in the region, who fear Beijing is seeking new leverage to advance its goals and raising the likelihood that an accidental encounter could escalate into conflict.

The U.S. confirmed earlier this year that China has reorganized its coast guard to serve as a military branch rather than answer to law enforcement authorities. Militarizing the formerly civilian organization provides China with the firepower to harass and intimidate vessels from other countries who dispute China's claims to waterways. The change, which Beijing denies, signals not only that China wishes to further its ambitions for its neighborhood, including seizing contested disputed territory and access to natural resources in East and South China seas but that it is becoming a more potent foe internationally.

"China still remains very adventurous, and [it is] expanding its actions into the East China Sea and South China Sea," a senior Japanese government official told U.S. News on the condition of anonymity. "We are still carefully studying the changes of the Chinese coast guard status."

The reorganization comes as Chinese President Xi Jinping has consolidated his power and positioned himself as the singular head of that chain of command. China has also begun mirroring how the U.S. military organizes itself through what it calls "joint operations" – or service branches working together in exercises or military activities – making it more effective across a broader swathe of regions and missions.

The Japanese defense ministry is focusing on coordinating better with its allies and partners to prepare for a potential confrontation, the official said, a task made more complicated now by the likelihood of a dispute over whether a vessel is operating under law enforcement rules or as an arm of the military.

Other countries, including the U.S., regularly employ their coast guards under military auspices but clearly spell out whether it is operating under wartime or civilian law.

Tokyo has not yet seen any specific changes yet in the posture or frequency of how China employs its coast guard fleet in that region, but it shares broader concerns about how it now could. A new report from a congressionally formed U.S.-China Economic and Security Review Commission assessed that China's use of its coast guard around contested islands and reefs "makes the sea force a more effective tool for Chinese coercion campaigns under the guise of 'maritime law enforcement' or 'maritime rights protection.'"

The annual report, released this month, adds that China denies any changes to the status of these forces, "creating a situation that increases the chance for miscalculation."

"They're on a journey of learning," says U.S. Navy Adm. Philip Davidson, commander of the headquarters that oversees all American military activity in the Pacific and East Asia. "I don't think we've seen everything we've wanted to see just yet."

Davidson described China as "moving quite perniciously with their money in the region." He shared concerns expressed by Vice President Mike Pence during a contentious summit with Asian leaders last weekend that Beijing's economic development and trading policy known as "One Belt, One Road" – or "Belt and Road" in the original Mandarin – would interfere in other countries' abilities to transit international shipping lanes freely.

"The key isn't two destroyers passing close to one another," Davidson said, referring to an incident in October in which a Chinese navy ship challenged a U.S. counterpart by passing within 135 feet of it. "It's the strategic threat that the closure of … freedom of navigation presents to trade."

He cited not only sea lanes but also the ability of citizens to travel by commercial airline, countries' ability to lay undersea cables and broader ability to communicate.

By contrast, a state-run newspaper in China printed a commentary this week calling for a greater civilian presence in its reclaimed islands in order to tamp down international concerns about China's ambitions. A report in Reuters quoted China's influential Study Times, which noted the "potential risk of war" in the region.