MANILA - A popular musician and activist who has been a vocal critic of President Rodrigo Duterte is being pilloried online after a sexually explicit video of him surfaced and went viral.

Although he initially claimed the video, in which he appears to be masturbating, was fake, Mr Jim Paredes later admitted in a blog that it was him.

"The video was real," he said. "There are already too many lies and liars in this world. I do not wish to be a part of that cabal."

He suggested that "in this ugly season of toxic politics, muckrakers determined to neutralise my influence by violating my privacy and digging up dirt on me are at work".

The video appears to be a Facebook live chat he was having with an unidentified partner.

Mr Paredes, 67, has criticised Mr Duterte on many occasions.

He called out Mr Duterte for telling soldiers last year to shoot women communist guerrillas in the vagina.

"You have no shame. You have no respect for women. You have a mother, a wife, a mistress and a daughter. They are women!" he said in a post on Twitter.

Mr Paredes also slammed Mr Duterte for his tirades against clergymen, and for calling God "stupid".

He suggested in a Twitter post that Mr Duterte probably has "dementia, psychosis, etc".

"Are you still in charge of your mental faculties?" he said.

Mr Paredes often attends and performs at anti-Duterte rallies. He has figured in heated exchanges with Mr Duterte's supporters, who have now turned to calling the singer a "hypocrite", "jerk" and "imbecile".

Ms Krizette Laureta Chu, a newspaper editor who rallies thousands of Mr Duterte's supporters on her Facebook page, said Mr Paredes has "lost (his) moral high ground to lecture the President about being 'bastos' (rude)".

GetRealPhilippines, a pro-Duterte blog, said: "Before this circus, Jim Parades personified everything that today's... opposition aspires to pitch itself as to the Filipino voting public - straight, uppity, and 'decent'... Then again, in the aftermath of the circus, it can still be argued that Paredes continues to personify today's... opposition: a community whose members are consistent in their inconsistency when measured using the very noble principles they espouse in their political rhetoric".

Mr Paredes is a known supporter of former president Benigno Aquino, having been an activist in the years leading to the ouster of the late dictator Ferdinand Marcos.

His brother served as press secretary of democracy icon Corazon Aquino, Mr Aquino's mother, who was president from 1986 to 1992.

He composed what is regarded as the anthem of the military-backed "People Power" revolt in 1986 that forced Mr Marcos and his family and cronies to flee to Hawaii.

Mr Paredes is considered an icon of the Philippine music industry.

As part of the musical trio APO Hiking Society, he helped define Filipino music in the 70s and 80s.

The band's music catalogue of some 40 albums released over 40 years is a mainstay of a genre labelled as "Original Pilipino Music".

Most of APO's songs were lighthearted takes on what it was like growing up during the years when Marcos held sway with an iron fist over the Philippines. Some were subtle jabs at the dictatorship.

In his blog, Mr Paredes apologised to "those who hold me in high esteem", adding: "I have never tried to project myself as perfect… I am a flawed person, a human being, much like everyone else. I made a mistake. I was irresponsible, and I am truly sorry."