Van Viet Tran was found dead on Saturday following the clash with members of the kidnapping group in the strife-torn island group, Brigadier General Cirilito Sobejana said.
A soldier was also killed and 15 other troops wounded while the Abu Sayyaf suffered undetermined casualties, said Sobejana who heads a special anti-terror task force.
“He (the Vietnamese) was hit by a bullet. Two things may have happened: he was hit during the encounter or he may have tried to take advantage of the situation (to escape) and then his abductors shot him,” he said.
He said militants were holding Van and four other Vietnamese apparently kidnapped at sea in Sulu.
Six other Vietnamese seamen were also being held on Basilan island, near Sulu, but two of them were beheaded last week.
Abu Sayyaf militants have been seizing hostages for ransom for years, often targetting foreigners such as seamen passing through the waters of southern Philippines.
The group, blamed for the worst terror attacks in the country’s history, is known to behead its hostages unless ransom payments are made.
German Jurgen Kantner, 70, was beheaded in February after the kidnappers’ demand for 30 million pesos ($600,000) was not met.
Last year, the Abu Sayyaf also beheaded two Canadian hostages.
The Abu Sayyaf, originally a loose network of militants formed in the 1990s with seed money from Osama bin Laden’s Al-Qaeda network, has splintered into factions, with some continuing to engage in banditry and kidnapping.
One faction led by Isnilon Hapilon has pledged allegiance to the Islamic State group and its members are among the hundreds of militants who have been occupying parts of Marawi for almost two months.
A massive military operation has been launched against them. (Agence France Presse)