A Philippine senator has described President Rodrigo Duterte as a "sociopathic serial killer" who is unfit to lead the country.

In a bid to force the president out of office, former justice secretary Leila de Lima called on the cabinet to rule him "mentally incapacitated".

Image: Ms de Lima has called on the cabinet to declare Mr Duterte as 'mentally incapacitated'

Referring to the People Power Revolution that toppled Philippine dictator Ferdinand Marcos in 1986, she said: "Now the time has come again for us to be brave and stand up to another criminal dictator and his evil regime."

She also compared Mr Duterte to Batman's foe, the Joker - calling him a "psychotic murderer" who led other villains in committing crimes.

Ms de Lima is currently facing arrest on drug charges.


Rights groups claim the charges have been fabricated to silence her and warn off other critics.

Image: Mr Duterte has called his crackdown on drugs 'a cleansing, a purge'

A spokesman for the president described her comments as "colourful language" and pointed out that Mr Duterte would allow public demonstrations against him.

Since being elected to office last year, the 71-year-old leader has been fighting a war on drugs, resulting in the deaths of tens of thousands of people.

The crackdown - which he has described as "a cleansing" - has resulted in the police reportedly killing 2,555 drug suspects, with about 4,000 other people murdered in unexplained circumstances.

Image: Police have arrested more than 40,000 suspects in the anti-drugs campaign

Amnesty International has warned police actions in the drug war may amount to crimes against humanity.

Ms de Lima's comments come a day after a retired Philippine policeman claimed that Mr Duterte ordered "death squad" hits to kill criminals and opponents while he was mayor of Davao city.

He is the second man to go public with claims of being part of a paid Davao death squad, dating back to 1988, when Mr Duterte became mayor of his hometown.

Survivor challenges Philippines President's drugs war

The extrajudicial killings allegedly included a radio show host who was a critic of the then-mayor, a pregnant woman and a four or five-year-old boy.

The president's office called the retired policeman's claims a "character assassination" and "vicious politics", insisting all such allegations had been proved false by independent agencies.

Over the years, the president has variously denied and confirmed the existence of a Davao death squad, and claimed to have personally killed people to set an example for police.