China in early May dispatched an oil rig to waters claimed by both the Chinese and Vietnamese governments. A second rig was reportedly sent to the region last week.
Both sides have met in Hanoi to discuss the situation, though each side blames the other for the lingering tensions. The official Vietnam News reported Sunday surveillance vessels were still operating within 10-12 nautical miles of the first rig.
"[They] conducted communication actions requesting the Chinese side to withdraw the rig and ships from Vietnamese waters," the Sunday report said.
The report said Chinese vessels positioned around the rig fired water cannons and rammed Vietnamese boats in the region, causing "many" injuries.
Pro-government China Daily published a Sunday editorial suggesting Vietnam was painting itself as the victim in the lingering dispute.
In a Friday briefing with reporters, U.S. State Department spokeswoman Jen Psaki said peace and stability in the region is a U.S. national interest.
"If a rig were placed in disputed waters, that would be a concern," she said.