Chinese oil rig Haiyang Shi You 981 (C) is seen surrounded by ships of China Coast Guard in the South China Sea, about 210 km (130 miles) off shore of Vietnam May 14, 2014.
The White House said on Wednesday that a dispute between China and Vietnam that erupted within days of President Barack Obama's visit to Asia to address regional tensions needs to be resolved with dialogue, not intimidation.
While the United States was not a party to the dispute, White House spokesman Jay Carney said Obama had repeatedly stressed on his trip last month the need for peaceful dialogue on various disputes involving China and the South China Sea.
The renewed tension between Vietnam and China underscores one of the biggest challenges in Asia facing Obama, who is under pressure by America's allies to accelerate a "pivot" of military assets to the region to counter China's rising influence.
Russia's annexation of Ukraine's Crimea peninsula - and perceptions of limited U.S. options to get Moscow to back down - have heightened unease in parts of Asia over whether Beijing will be emboldened to use force to pursue its territorial claims in the East and South China Seas.
Such disputes "need to be resolved through dialogue, not through intimidation," Carney told a regular briefing. "We again urge dialogue in their resolution."
An Asian diplomat said it was important that Washington took a firm line with Beijing while also using its influence with Vietnam to calm the mood.
He said the concern among Southeast Asian countries was that China was seeking incremental gains in provoking a series of crises with its neighbors, a tactic that could eventually change the regional landscape unless it was met with a resolute response.
The White House statement comes as Obama's policy toward Asia has come under some criticism at home for being more rhetoric than substance.
The current crisis erupted within days of a week-long visit to Asia by Obama in late April in which he pledged that Washington would live up to its obligation to defend its allies in the region.
The foreign minister of Singapore, a close US ally and one of Vietnam's partners in the Association of Southeast Asian Nations (ASEAN), said in a speech in Washington on Tuesday that China's rapid rise had already changed the regional dynamic.
"I note that the US is trying to urge all claimants not to resort to aggression and has called for a reduction of tensions," the minister, K. Shanmugam, said.
"To some extent, this reflects the new reality. The U.S. now needs the co-operation of others and asks for it. As opposed to the post World War Two situation, when the U.S. could impose its will."