China's actions in the South China Sea were an example of it trying to gain territorial space through force, and were destabilising the region, a senior U.S. admiral said on Tuesday.
The Philippines and China have had a series of maritime run-ins, including water cannon use, and heated verbal exchanges that have triggered concern about an escalation at sea.
Admiral John Aquilino, Commander of the U.S. Indo-Pacific Command, said in an address to the Lowy Institute think tank in Sydney that China's actions against the Philippines, particularly in Second Thomas Shoal, were "dangerous, illegal and they are destabilising the region".
Aquilino said he was "very concerned about what is happening at Second Thomas Shoal", where the physical action of the Chinese coast guard and a fishing vessel had resulted in six sailors injured.
"So what's next and how far are they willing to go in that area?"
He said similar actions by China were also being seen elsewhere in the region, including in Japan and Malaysia.
"This is not isolated, this is about the PRC (People's Republic of China) trying to gain territorial space unilaterally through force," he said.
China claims almost the entire South China Sea as its territory, policed by an armada of coastguard vessels, some more than 1,000 km (620 miles) from its mainland, and has maintained its responses have been appropriate in the face of Philippine encroachment.
Aquilino said there was positive movement in the U.S-China relationship since the leaders of the two countries had spoken, with no concerning maritime interactions between the U.S. and China since then.
Aquilino said he was concerned this detente was temporary, as China sought to stabilise its economy.
He also expressed concern about what he said was synchronisation between Russia and China, and Russia and North Korea.
"Those sets of cooperation and the linkages are really a new world and a concern," he said.
In the Pacific Islands, he said China was exercising economic coercion, and said Australia and the U.S. were working together to focus on increasing development assistance to the region, including the Solomon Islands which has struck a security pact with China.
"An increased military presence in that region is a direct threat to Australia as it applies to homeland defence and it doesn't put the U.S. in a good position either," he said.
