Philippines President Rodrigo Duterte may have ordered police to withdraw from his brutal drug war, but the bodies continue to pile up at a rate of 10 a day.

Shadowy assassins have killed nearly 150 people since the end of last month, human rights groups have said.

Duterte pulled police from his seven month 'war on drugs' on January 31. Official figures state 2,555 drug suspects were killed by law enforcers in this time, while 3,930 people were murdered in unexplained circumstances, prompting outrage over extrajudicial killings.

Police investigators at a crime scene where two alleged robbers were killed by police in Manila

A dead body is removed by coroners officers after a shooting by an unidentified gunman in Manila today

The latest police figures, given to AFP, show there were 4,076 'murder cases under investigation' on Monday this week.

The increase of 146 showed extrajudicial killings had slowed, but were nevertheless continuing in the drug war, activists believe.

'The targets are still the same, as far as we are concerned: people linked to drugs and who live in poor neighbourhoods,' Wilnor Papa, campaign official for the Philippine branch of Amnesty International said.

Papa said unknown assailants were now killing between nine and 10 people daily.

Police investigate a crime scene where two alleged robbers were shot dead by officers last week

Philippines President Rodrigo Duterte ordered police to withdraw from his war on drugs on January 31

This compared with about 30 people a day being killed by police and unknown assailants when officers were still leading the crackdown.

On Thursday police found four men shot dead inside a shanty in northern Manila, in a scene very similar to those covered at the height of the drug war.

Witnesses said gunmen broke into the house and started shooting, while three other men were shot dead in separate incidents elsewhere in the same district that night.

Duterte's order to end police involvement in the drug war came after rogue anti-drug officers kidnapped and murdered a South Korean businessman, Jee Ick-joo, inside the national police headquarters as part of an extortion racket.

A suspected drug dealer is found dead inside a house after being gunned down by mystery assassins in the capital of the Philippines

But Duterte promised the war would continue and more addicts, as well as traffickers, would be killed as he sought to eradicate drugs in society.

Amnesty published a report this month accusing police of systemic human rights abuses in the drug war, including gunning down defenceless people, paying assassins to murder addicts and stealing from those they killed.

It also said police were being paid by their superiors to kill.

Duterte has since ordered the much smaller Drug Enforcement Agency to lead the drug crackdown, with the support of the military.

Derrick Carreon, spokesman for the 1,791-member drug agency, told AFP there had been far fewer killings by authorities since it took charge, without giving figures.

'(But) there is no point in comparing these figures because the police is a much larger organisation, capable of conducting more operations,' Carreon said, adding the military had mostly acted as observers so far.

The national police force has 160,000 officers.