Extrajudicial killings in the Philippines could be attributed to "rivalry" among the members of drug syndicates, according to President Rodrigo Duterte.

In a taped message on Monday night, Duterte said he himself conducted a "discreet" inquiry on the alleged extrajudicial killings.

"And this extrajudicial killing, they have been harping for many years. Truthfully, I'm also doubting and there was a time when I conducted a discreet hearing why (was it happening)," he said.

"What reached me is that sometimes there is a rivalry of the turf, their territory, who is handling," Duterte said.

He said there were also who "absconded" the money while others stole the money at the street level.

Duterte said it is not his obligation to tell lies.

"If you believe, that's good. If not, that is not my problem. That is what is happening in the nation," he added.

Since Duterte assumed office in 2016, nearly 6,000 individuals who were allegedly involved in illegal drugs have been killed in police operations.

Local and international human rights groups have been condemning the alleged extrajudicial killings and have called for an investigation on the matter.

The Duterte administration has been refusing international fact-finding groups to conduct an investigation on the alleged extrajudicial killings in the country.

The government has been insisting that the legal system in the country has been working. Celerina Monte/DMS