The Second Thomas Shoal is currently occupied by the Philippines but is claimed by multiple other states including China. Recently there have been several clashes between China and the Phillipines over the atoll. The US is a treaty ally of the Philippines.
'killed' requires an physical act, specifically from one of the other countries mentioned in the question. In other words it doesn't count if someone dies for any other reason or they die in a way where it could be reasonably deemed that their own country killed them). It would count if another country took some action that clearly led to a death, ie a ship was sunk and survivors were not rescued.
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@WesleyJB it requires an act of violence, from one of the other states mentioned. Will update description