There was no immediate claim of responsibility for the attack, although military officials said they suspected a faction of the Moro Islamic Liberation Front, a separatist group fighting government forces in the area, may have been behind the attack.
However Eid Kabalua, a spokesman for the MILF, denied any involvement.
Maguindanao province has seen continued clashes between government forces and the MILF, displacing thousands of people in a conflict that has lasted for over 40 years.
Abu Sayyaf, another rebel group which Philippine officials say has links to al-Qaeda, was blamed for an ambush on Sunday in nearby Basilan island that killed seven police officers.
The Abu Sayyaf broke away from the MILF in the early 1990s, and has been blamed for a string of high-profile kidnappings and bomb attacks.
It has kidnapped dozens of foreigners, businessmen and aid workers over the past decade and is on the US government's list of foreign terrorist organisations.