Kerry was speaking ahead of talks today with a top figure in Vietnam's ruling communist party, Executive Secretary Dinh The Huynh (din tay hwin).
Vietnam is among governments claiming territory in the South China Sea, where China's assertive behavior and land reclamation has stirred tension.
The meeting comes five months after President Barack Obama visited Vietnam and lifted restrictions on arms sales to the former US enemy. It also takes place as longstanding US ally in Southeast Asia, the Philippines, is strengthening its ties with China.
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