I imagine China is backing the Philippines. I hope the US stays out of it.
well no both the US and China have been ambiguous at best, probably precisely because of the concern you raise, that them backing any side obviously would trigger the other side to step in, turning this from a territorial dispute into a full blown regional one.
The State department have issue the standard "we're sorry someone got killed, and won't get ahead of our self until full investigation, and hope both side restrain them self" type of politically correct statement. while China have made a mild condemnation of the Philippines (because this shit happens to Chinese boat as well, and there was that whole incident last year where a Hong Kong bus was hijacked in the Philippines and most of the hostage ending up dead in the hands of the Philippine Swat team, whom managed to kill more hostage than kidnappers, and hell, the resulting investigation seem to find that almost all of them died from the SWAT team and not the hostage :facepalm