The White House said on Thursday it would support the use of legal action by Vietnam against China to resolve a dispute after the deployment of a Chinese oil rig to disputed waters in the South China Sea.
Vietnamese Prime Minister Nguyen Tan Dung said, in comments to Reuters, his government was considering various "defense options" against China, including legal action.
U.S. support for such a move would likely upset Beijing.
"The United States has a national interest in maintenance of peace and stability; respect for international law; unimpeded lawful commerce; and freedom of navigation and over flight in the South China Sea," White House spokesman Patrick Ventrell said in response to questions about the prime minister's remarks.
"The United States supports the use of diplomatic and other peaceful means to manage and resolve disagreements, including the use of arbitration or other international legal mechanisms."
Dung's comments, given in a written response to questions from Reuters, were the first time he has suggested Vietnam would take legal measures, and drew an angry response from China, which insisted the rig was in its sovereign waters.
China accused Vietnam of stoking regional tensions.
Reporting by Roberta Rampton and Jeff Mason