Philippine President Rodrigo Duterte inspects a police honour guard

Philippine President Rodrigo Duterte on Wednesday announced "dead-or-alive" bounties worth $40,000 each for policemen he accused of helping an accused narco-politician, and said he prefered they be killed.

The call for police officers to kill their colleagues is the latest inflammatory comment by Duterte in his controversial drug war, which has claimed thousands of lives, and comes shortly after a meeting with US Secretary of State Rex Tillerson.

Duterte made the offer during a speech at national police headquarters, offering two million pesos ($40,000) for an unspecified number of officers who allegedly helped a mayor killed in an anti-drug operation on July 30.

"Each of those policemen carry on their heads now, I am announcing, two million per head and you are free to go on leave (to pursue them)," Duterte told the officers in the audience.

"I'll cut short my speech so that you will have a chance for a crack at the two million for those idiots."

Duterte added the bounty would be paid if the policemen were found "dead or alive -- better dead".

He said the unidentified policemen had worked with Reynaldo Parojinog, the mayor of the southern city of Ozamiz, who was killed in the pre-dawn raid along with his wife, his brother and 13 other people.

Police said they were forced to kill the 16 people in self-defence, but Parojinog's lawyer has insisted the mayor and others had not resisted arrest.

Duterte had accused Parojinog of being a major drug trafficker.

As he has done in similar cases of alleged extrajudicial killings, Duterte on Wednesday also vowed to give legal protection to the policemen who killed Parojinog and the other 15.

If they were found guilty of murder, he would pardon them, he vowed.

Duterte easily won presidential elections last year after promising an unprecedented war on drugs in which tens of thousands of people would be killed.

Since he took office in the middle of last year, police have confirmed killing more than 3,400 people in anti-drug operations.

More than 2,000 other people have been killed in drug-related crimes and thousands more murdered in unexplained circumstances, according to police data.

Rights groups say many of those victims have been killed by government-backed vigilantes, and Duterte has boasted that he would be "happy to slaughter" three million drug addicts.

Former US president Barack Obama was among the many international critics of Duterte's tactics.

But criticism from the United States, the Philippines' former colonial ruler and mutual defence partner, has been toned down under the administration of Donald Trump.

Tillerson met Duterte in Manila on Monday on the sidelines of a regional security forum. Duterte said American officials did not raise any concerns with him.