At least 14 marines were killed and 10 of them beheaded in a fight with Muslim militants in southern Philippines, the military said on Wednesday.
Nine marines were also wounded in the nine-hour clash Tuesday in Tipo-Tipo town in Basilan province, 900 km south of Manila.
Brigadier General Ramiro Alivio, marine brigade commander in Basilan, said 10 marines who went missing after the firefight were found dead early on Wednesday.
He said that attackers who included members of the Abu Sayyaf rebel group and the separatist Moro Islamic Liberation Front beheaded the 10 marines.
"It was raining hard and that made the movement of the soldiers quite difficult. We were outnumbered, that's why we suffered heavy casualties," he said.
Lieutenant Colonel Ariel Caculitan, a marines spokesman, said the other four fatalities occurred during the firefight.
"We were totally outnumbered and we had no time to recover any enemy casualties, but we have reports of dead and injured on their side," Caculitan said.
The marines, numbering about 50, had encountered around 300 Muslim rebels while on an operation to verify reports that abducted Italian priest Giancarlo Bossi was being held in the province.
Bossi, 57, was abducted June 10 in Payao town in nearby Zamboanga Sibugay province. He was the third Italian priest kidnapped in the southern Philippines in the past 10 years.