THE world’s most straight-talking leader Philippines’ President Rodrigo Duterte has gravely warned human rights campaigners to stop interfering in his war on drugs.

Duterte issued his warning as the death toll from his controversial crackdown climbed above 4800, or roughly an average of 30 deaths a day since it began five months ago.

“The human rights (defenders) say I kill. If I say: ‘Okay, I’ll stop’. They (drug users) will multiply,” Duterte said.

“When harvest time comes, there will be more of them who will die. Then I will include you among them because you let them multiply.”

Amnesty International Philippines was among a range of groups to speak out against the comments, saying it was “appalled”.

“This pronouncement is ... inciting hate towards anyone who expresses dissent on his war against drugs,” it said in a statement.

The National Alliance against Killings Philippines, a newly formed coalition of rights groups, said it took the threat very seriously and called on Duterte to revoke it.

“His comment — that human rights is part of the drug problem and, as such, human rights advocates should be targeted too — can be interpreted as a declaration of an open season on human rights defenders,” it said.

Father Atilano Fajardo of the archdiocese of Manila, who works with urban poor groups, said those seeking to protect the vulnerable would not be intimidated.

“This (threat) is a continuation of his effort to create a culture of fear, a culture of violence. We will not let this come to pass,” he told AFP.

Fajardo said the Catholic Church, which counts more than 70 per cent of Filipinos as followers and has so far been subdued in its criticism of the drug war, was starting to find its voice on the issue.

“That is why he is more threatening. He cannot just frighten us. The priests and nuns will speak out,” he said.

Duterte won presidential elections in May after pledging to kill tens of thousands of drug suspects, warning that otherwise the Philippines would turn into a narco-state.

Since assuming office, he has called on police and even civilians to kill drug users.

Duterte also said he would be “happy to slaughter” three million drug addicts, and likened his campaign to Nazi leader Adolf Hitler’s efforts to exterminate Jews in Europe.

The 71-year-old lawyer later apologised for his Hitler reference, but said he was “emphatic” about wanting to kill drug users.

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Duterte visited the remote mountain town of Butig, in the troubled southern Philippines island of Mindanao, which is 800km south of Manila, on Wednesday. It has been partly occupied by the Maute, an armed Muslim extremist group that has previously pledged allegiance to the Islamic State movement in Syria and Iraq.

Duterte after speaking to military officers and meeting with wounded soldiers, had a warning for the Maute as he spoke before troops.

“For those who fight the government, don’t wait for the hands of the clock to reach the 25th hour and the bells will toll. I can be harsh so I could command obedience as I can, and I am not afraid,” Duterte said.

He said if the Maute resisted, he would be “harsh”

“As harsh I can ever be,” Duterte warned.

“I do not want to wage war but do not force my hand to do it.”

Military spokesman Major Filemon Tan said 85 to 90 per cent of Butig had been recaptured from Maute which the group seized last Thursday with 61 of the extremists killed and 12 wounded, compared to 35 injured on the government side. Intense aerial and ground bombing has taken place in the mountains.

“They have to go on with the operation,” Duterte said.

“What is there to stop? Nobody is showing their sincerity there. So the fight goes on.”

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Muslim groups have waged a decades-long armed independence struggle in the south of the mainly Catholic Philippines that is believed to have claimed more than 120,000 lives.

On Monday, Duterte said IS, which had controlled vast swathes of Iraq and Syria, had linked up with the Maute gang, a departure from previous military denials of formal links between IS and local extremist groups.

Maute members are believed responsible for an attempted bombing near the US embassy. Two men have been detained and “three to five other suspects” are still being hunted over the powerful bomb found planted in a trash can near the US embassy in Manila on Monday.

“There is a real possibility that this is the handiwork of the Maute group,” Manila’s head of police, Chief Superintendent Oscar Albayalde, said.

He described one man, who was arrested in Bulacan province just outside the capital, as a Muslim convert and the other, detained in a Manila residential area, as a Muslim.

Maute extremists have also been blamed for a bomb that injured seven military bodyguards of President Duterte and two other soldiers in Mindanao on Tuesday.