China in early May sent an oil rig to waters disputed by the government of Vietnam. The Vietnamese government said Chinese vessels around the rig are harassing nearby Vietnamese ships on a daily basis and have since expanded their zone of protection.
"Previously, Chinese vessels protecting the oil rig operated within 5-6 nautical miles around the platform, but they have now expanded their ranges of operation to 8 nautical miles," Nguyen Ngoc Oai, the head of Vietnam's Fisheries Surveillance Department, told Voice of America's Vietnamese service Wednesday.
China says it's been operating in its territorial waters, though Vietnam has said its sovereignty was violated and it has a right to protect its national interests.
The Vietnamese official said Chinese ships near the rig rammed a surveillance vessel Wednesday, causing some structural damage but no injuries.
The U.S. government, which owns VOA, said it has no stance on the territorial dispute, though it views China as the aggressor.