Philippine President Rodrigo Duterte defended his bloody anti-drug campaign on Monday, saying the nearly 1,800 deaths in two months didn't compare with brutality in Syria or atrocities committed by Islamic State group extremists.

"I did not kill any child. I did not drop barrel (bombs) like (Syrian President Bashar) Assad," Duterte said in a speech marking National Heroes' Day. "I'm fighting ... criminals."

Referring to Islamic State group militants, whom he called "idiots," Duterte said, "I do not burn women because they refuse to have sex."

At least 1,779 drug suspects have been killed in Duterte's campaign, including 712 who were gunned down in clashes with police, with the rest being slain in still-unclear circumstances, the national police chief told a Senate inquiry last week.

Duterte said at least 3.7 million Filipinos have become addicted to methamphetamine, a stimulant known locally as shabu, with about 600,000 drug users and dealers surrendering to authorities.

Human rights groups have expressed alarm over the killings, and U.N.-appointed human rights experts have warned that steps should be taken to halt the violence, adding that the government and law enforcers could be held responsible.

"Claims to fight the illicit drug trade do not absolve the government from its international legal obligations and do not shield state actors or others from responsibility for illegal killings," U.N. Special Rapporteur on summary executions Agnes Callamard said in a statement this month.

Duterte, 71, who took office June 30, built a name with a deadly crime-busting style as the longtime mayor of southern Davao city. He described his campaign against drugs as a harsh war that would involve the military because the problem is now a crisis and claimed the lives of law enforcers.

"We might still end up like the South American countries and their fractured governments. I am declaring war," he told the audience that included ambassadors, war veterans and security officials. The drug menace, he said, "has infected every nook and corner of this country involving generals, mayors, governors, barangay (village) captains" and policemen.

Pressing his campaign, Duterte announced bounties of 2 million pesos ($42,000) for information that would help the government identify any police officer protecting drugs syndicates.

He repeated his pledge to defend the police and military, but warned law enforcers against conniving with criminals.

"In the pursuit of law and order, pursuant to my directions, you do not have to worry about criminal liability," he said. "I will go to the prison for you. I take full legal responsibility, you just do it according to the books."

"But for those in government, the police, the corrupt police and the corrupt judges and the corrupt prosecutors, there will be a day of comeuppance, there will always be a day of reckoning," Duterte said.

On Monday, an unidentified gunman killed a suspected drug lord, Melvin Odicta Sr., and his wife after they got off an inter-island ferry in central Aklan province, police said. The killer escaped.

Odicta, a wealthy businessman who owned a fleet of taxis, a bar and a restaurant, denied involvement in the illegal drug trade when he and his wife met officials in Manila last week.

Asked about Odicta, Duterte told reporters the slain man was a leading suspected drug lord in the central Philippines. "He really got unlucky. Who wants to step in next after Odicta?" Duterte asked.