BEIJING, July 4 (Xinhua) -- A Chinese Foreign Ministry spokesman on Friday confirmed that the coast guard had detained a Vietnamese fishing vessel and six crew for illegal operations in the South China Sea.

Hong Lei said the Vietnamese boat was detained on the morning of July 3 within Chinese territorial waters, 7 nautical miles south of Sanya, Hainan Island.

Chinese authorities are investigating the case .

China has repeatedly asked Vietnam to strengthen regulations and education of its fishermen to prevent such incursions into Chinese waters.