Two snorkelers a Frenchman and a Russian drowned in waters off the central Vietnamese province of Binh Thuan on Monday, police said. Their companion, a Russian, was rescued the same day.
A Russian, identified only as Pavel, was found floating unconscious by local fishermen. When he regained consciousness, he pointed out that two fellow-snorkelers were missing. The fishermen then found the bodies of Philippe Bousseau, 47, and Alexander A Nikolav, 42.
The three tourists were snorkeling in waters around the Cau Island.
Bousseau had been staying at the Viet Phap Resort in Ham Thuan Nam District and Nikolav at the Hai Au Resort in Phan Thiet Town. Binh Thuan is a popular tourist destination famed for its sand dunes and beach resorts in Mui Ne.
The two dead tourists may have been killed in a blast caused by fishing explosives, Phan The Nam, an officer with the provincial police force told AFP on Wednesday.
Pavel told investigators that he heard an explosion before losing consciousness.
"According to our initial information, it is probable that certain people threw explosives for fishing into the water," Nam said.
Nam said the deaths were being investigated, but noted the victims were not snorkeling in a designated area. "We haven't yet determined the cause of their death. We are examining their bodies and the accident scene," he said.
Using explosives for fishing is banned in Vietnam.