The Philippine police have received cash payments for executing drug suspects, planted evidence at crime scenes and carried out most of the killings they blame on vigilantes, said two senior officers who are critical of President Rodrigo Duterte's "war on drugs."

In the most detailed insider accounts yet of the drug war's secret mechanics, the two officials challenged the government's explanations of the killings in interviews with Reuters, speaking on the condition of anonymity.

Almost 9,000 people, many of them small-time users and dealers, have been killed since Duterte took office on June 30. Police say about a third of the victims were shot by officers in self-defense during legitimate anti-drug operations. Human rights monitors believe many of the remaining two-thirds were killed by paid assassins operating with police backing or by police disguised as vigilantes.