The US State Department said it was monitoring events in Vietnam closely, and urged restraint from all parties.
White House spokesman Jay Carney said:
We support the right of individuals to assemble peacefully to protest.
(Such disputes) need to be resolved through dialogue, not through intimidation
We again urge dialogue in their resolution.
The current crisis erupted within days of a week-long visit to Asia by President Barack Obama in late April in which he pledged that Washington would live up to its obligation to defend its allies in the region.
More top news
A mother died after trying to save her three-year-old son when he fell down a cliff during a family hike.
The Government's Universal Credit reform has "serious" flaws that need resolving before it is rolled out, a new report has said.
Leicester City's unlikely Premier League success features on the front pages of many of Tuesday's national newspapers.