China sent a survey vessel through waters claimed by its maritime sovereignty rival Vietnam this month to warn Hanoi against starting new energy exploration projects and filing any motions in an international court, observers say. This follows the passage of another Chinese vessel near Vietnam in April and a standoff at sea last year. Collin Koh, a maritime security Research Fellow at RSIS, said the recent moves are meant to signal for Vietnam to think twice before undermining Chinese interests, and that includes striking up new deals with other energy partners.