Philippines President Rodrigo Duterte says his government is willing to face any inquiry into the deaths of hundreds of suspected drug criminals as human rights groups express alarm over the extrajudicial killings.

Nearly 600 suspected drug peddlers and users have been killed in police operations since Mr Duterte took power six weeks ago, police say, but rights groups put the number at more than 1,000.

"We are willing to submit ourselves for an investigation before anybody," Mr Duterte said in a speech at the national police office.

He said some of the killings were carried out by drug gangs and not police officers.

"The fight against drugs will continue unrelenting until we have destroyed the apparatus operating in the entire country," he said.

The President also cautioned police against using excessive force in making arrests.

"I myself, who ordered the campaign against drugs, take full and sole responsibility for it," Mr Duterte said.

"Do not kill if you're not in danger of losing your life."

Public inquiry into drug killings to begin next week

Senator Leila de Lima, head of the Senate panel on justice and human rights, will open a public inquiry next week into drug-related killings and has summoned senior national police and anti-narcotics officials to explain the anti-drug campaign.

There have been cases when police officers have killed suspected drug dealers in handcuffs, in police custody or inside prison cells, civil rights lawyers said.

Police have said they will not condone wrongdoing but that some may have been killed by rogue officers.

Mr Duterte won the presidency in May on a single platform of suppressing crime and drugs, declaring a war on narcotics on his first day in office.

He has identified 160 officials, police and judges in a name-and-shame campaign to stop the drug trade.

Reuters