The action followed clashes between demonstrators and police on U.S. campuses and a blockade at Paris's Sciences Po university
Police said the clashes occurred in the early hours of the day in Mamasapano town.
Restituto Padilla, spokesperson of the Armed Forces of the Philippines, said army soldiers were later deployed to retrieve the body of the slain policemen. He said the military retrieved bodies of "nine out of the more than 30 (policemen) killed".
While the military helped in extricating police casualties, the policemen were conducting operations against lawless elements and carrying out a warrant of arrest, Padilla added.