The United States will continue to closely cooperate with Vietnam, a U.S. official said after Hanoi announced last week strengthened ties with China, including on defence and security, as the two great powers compete for influence. Vietnam's leaders upgraded relations with Beijing during China's President Xi Jinping's visit to Hanoi last week, three months after they had boosted ties with Washington as Joe Biden travelled to the country in what has been seen as a success for Vietnam's "Bamboo di