MANILA (Reuters) - Philippine senators have criticized the way President Rodrigo Duterte is carrying out his anti-narcotics campaign, saying it should be done within the bounds of the law and he must punish erring police officers.

Philippines' President Rodrigo Duterte gestures as he speaks during a solidarity event with urban poor community in Mandaluyong city, Metro Manila, Philippines December 7, 2016. REUTERS/Ezra Acayan

Police say 2,004 people have been killed by officers in self-defence during anti-drug operations since the president took office on July 1. Another 3,060 killings have been classified as “under investigation”.

Senators said while they had found no clear proof that the rising number of extrajudicial killings was state-sponsored, they told Duterte to observe due process and give the accused their day in court.

Duterte has denied the police are conducting extrajudicial killings.

But at the same time, he has welcomed the death toll. In September, he said he’d be “happy to slaughter” three million drug addicts.

The president has repeatedly told the police to “kill” accused drug dealers if they violently resist, or if officers feel their lives are in danger.

“The war against illegal drugs must be won within the legal system, and the president must lead in reminding the people of this important message,” the senators said in a report after conducting an inquiry into extrajudicial killings.

The senators, including the president’s allies, also cautioned the unpredictable Duterte to be “careful with his words (and) avoid inappropriate statements lest they be construed as policies of the state.”

The president’s spokesman and communications secretary were not available for comment on the report.

Duterte won a May election on a promise to wipe out drugs and dealers.

Amid concerns human rights groups about the surge in drug-related killings, Duterte has repeatedly defended the police, saying he was willing to go to jail for them.

On Wednesday, Duterte defended police officers who killed a detained mayor on a list of top drug suspects even after another law enforcement agency concluded the death was an extrajudicial killing.

“When the police deem themselves to be omnipotent, they are emboldened and more killings ensue; the duty to protect the people is thrown out the window,” the senators said in their report, a copy of which was obtained by Reuters on Friday.

“The offshoot will be silencing accused drug pushers and drug lords without affording them the bill of rights guaranteed to them by the constitution.”

The president must raise police standards and accountability, they said.

“When the police violate the law, they must be punished,” they said.

“The time to act and end the impunity of killing is now,” the senators said.