The slain officer was initially identified only as 1Lt. Bula, who died on the spot from multiple gunshot wounds.
Bula’s companion, an enlisted Marine, was also killed in the attack.
The two soldiers belonged to the 8th Marine Batallion Landing Team (8MBLT).
Lanao del Sur’s police command said the slain Marines, along with their companions, were on their way to Maguindanao from their base in a remote town in Lanao del Sur when the rebels, positioned at both sides of a critical stretch of the Secretary Narciso Ramos Highway, opened fire with automatic weapons and B-40 rockets.
The encounter happened at the junction of Barangay Purakan in Balabagan town.
Police investigators said they are now confirming reports by civilians that three other passengers who jumped out of the vehicle were missing and the subject of an extensive search by local authorities.
Southern Command chief Lt. Gen. Roy Kyamko directed his men to get the perpetrators "at all cost."
The slain Marines were brought to a funeral parlor here by personnel of the 1st Marine Brigade based in Marawi City, in preparation for the airlift of their remains to the headquarters of the Philippine Marine Corps in Fort Bonifacio.
Sources in Lanao del Sur’s religious community said the government’s peace panel should help investigathe identities of those behind the ambush, convinced that the attack could be a test mission for Moro fighters who have just finished guerrilla training at the border of Lanao del Sur and Maguindanao. — With Roel Pareño, Jaime Laude