The dispute centers on the Spratly Islands, a rocky archipelago without confirmed oil or gas reserves that is also claimed wholly or partially by Brunei, Malaysia, the Philippines, and Taiwan.
The United States has refused to take sides and is calling for a legal resolution to the competing claims.
“We support the expansion of economic ties between the United States and Vietnam, including growing investment activity by U.S. firms,” a State Department spokeswoman said. “The United States does not take sides on the legal merits of the competing sovereignty claims in the South China Sea. We object, however, to any attempt to pressure U.S. firms operating in that area.”