U.S. plans to send warships or military aircraft within 12 nautical miles of China's artificial islands in the disputed South China Sea, possibly within days, could open a tense new front in Sino-U.S. rivalry.
A range of security experts said Washington's so-called freedom of navigation patrols would have to be regular to be effective, given Chinese ambitions to project power deep into maritime Southeast Asia and beyond.
But China would likely resist attempts to make such U.S. actions routine, some said, raising the political and military stakes. China's navy could for example try to block or attempt to surround U.S. vessels, they said, risking an escalation.
Given months of debate already in Washington over the first such patrol close to the Chinese outposts since 2012, several regional security experts and former naval officers said the U.S. government might be reluctant to do them often.
U.S. allies such as Japan and Australia are unlikely to follow with their own direct challenges to China, despite their concerns over freedom of navigation along vital trade routes, they added.
"This cannot be a one-off," said Ian Storey, a South China Sea expert at Singapore's Institute of Southeast Asian Studies.