MANILA (Reuters) - Philippine police killed 32 people in dozens of anti-drug operations in a province north of the capital, Manila, in the single deadliest day of President Rodrigo Duterte's unrelenting war on drugs.

About 109 petty criminals, including street-level drug peddlers were arrested and dozens of guns seized in police operations across Bulacan province from Monday night until Tuesday afternoon, said provincial police chief, Romeo Caramat.

"We have conducted 'one-time, big-time' operations in the past, so far, the number of casualties and deaths, this is the highest," Caramat told a news conference.

He defended police action and said the deaths were during shootouts, and were not executions, as activists have often alleged.

"There are some sectors that will not believe us, but, we are open for any investigation. All we can say is that we don't have any control of the situation. As much as possible, we don't want this bloody encounter."

Thousands of people have been killed in the anti-drugs campaign, Duterte's signature policy, since it was launched on June 30 last year, most users and small-time dealers from poor neighborhoods.

The intensity of the crackdown has alarmed the international community, and activists and human rights groups say police have been executing suspects and planting drugs and guns at crime scenes. Police and the government officials reject that.

Police also deny involvement in thousands of murders by mysterious gunmen, blaming them on gang turf wars, drug dealers silencing informants, or vigilantes targeting drug users.

"There were 32 killed in Bulacan in a massive raid, that's good," Duterte said in a speech.

"Let's kill another 32 every day. Maybe we can reduce what ails this country."

Police conducted 49 sting drug operations in Bulacan that resulted in about 20 armed encounters, Caramat said. Ten other gunfights ensued when police tried to serve arrest warrants to suspects who fought back.

He said 93 of those held were wanted for other crimes, as well as drugs offences.

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Bulacan has been a major target in the drugs war, with some 425 people killed and 4,000 offenders arrested, according to Caramat, making it the second-biggest hot spot in the crackdown outside of the Manila area.

Political opponents of Duterte have filed a complaint with the International Criminal Court (ICC) accusing the president and top aides of crimes against humanity, arguing they failed to address allegations of widespread police abuses that have been brought to their attention.

Duterte has welcomed the ICC complaint, and said he was willing to rot in jail to protect Filipinos.

He has often complained about human rights groups criticizing and undermining his campaign and on Wednesday said he would instead investigate them, or worse.

"If they are obstructing justice, shoot them," he said.

(Reporting by Manuel Mogato and Karen Lema; Editing by Martin Petty, Robert Birsel)