Philippine former president Benigno Aquino was laid to rest in a Manila cemetery on Saturday beside his parents, two of the Southeast Asian country's democracy icons.

The money became a source of controversy during Aquino's term from 2010-2016, with critics claiming he used it to barter for favours from legislators.

The Philippines' anti-graft body filed criminal charges against former President Benigno Aquino on Wednesday for mishandling a botched anti-militant raid that resulted in the death of 44 police commandos in 2015.

Rodrigo Duterte was sworn in as the Philippines' 16th president on Thursday, capping an unlikely journey for a provincial city mayor whose brash man-of-the-people style and pledges to crush crime swamped establishment rivals in May's election.

Philippines President Benigno Aquino on Sunday appealed to Filipinos to defend their freedom and democracy and remain vigilant as he warned the horrors of martial law under the late Ferdinand Marcos could happen again.

Rodrigo Duterte became the 16th president of the Philippines on Monday when a joint session of Congress declared him winner of a May 9 election, succeeding Benigno Aquino.

Philippine President Benigno Aquino warned on Saturday the frontrunner in the race to replace him carried similar dangers to Hitler and would bring terror to the nation.

The Philippine Supreme Court ruled Tuesday a military accord with the United States was constitutional, paving the way for a greater presence of US forces in the former American colony as tensions simmer in the South China Sea.