Prime Minister Nguyen Tan Dung addressed delegates gathered in Myanmar for a summit for the Association of Southeast Asian nations. China's decision to send an oil rig to disputed waters, he said, was a national security concern.
"Peace, stability, security, and freedom and safety of navigation and aviation in the East Sea, the common interest of ASEAN, the region, and the world, is under serious threat," he said Sunday.
In early May, state-run China National Offshore Oil Corp. positioned an oil rig about 120 miles off the coast of Vietnam in waters claimed by both China and Vietnam. The prime minister said Chinese vessels have acted aggressively toward Vietnamese boats near the area of dispute.
The Chinese government has said it's operating in its territorial waters, adding it was surprised by Vietnam's reaction. The Vietnamese government, however, says China is in violation of a 2002 treaty governing conduct in the South China Sea.
China is at odds with its regional neighbors over claims to territory in the South China Sea.