The Philippines' national police chief said on Tuesday that about 1,900 people had been killed during a crackdown on illegal drugs, which began seven weeks ago when President Rodrigo Duterte took power, but about 40 were not drug-related.

The number provided by Director-General Ronaldo dela Rosa at a Senate hearing was higher than the 1,800 deaths he gave at the hearing on Monday. He gave no explanation for the higher number but said the figures were updated.

It means that on average, 35 people have been killed each day since Duterte came to power.

Dela Rosa said about 750 of the dead were killed in police operations against drug peddlers. The other deaths were being investigated, he said.

‘Not all deaths under investigation are drug-related,’ dela Rosa said, adding that 40 killings were known to be due to enmity or robbery.

Nearly 700,000 drug users and drug peddlers have turned themselves in to escape the crackdown, dela Rosa said. He said there was a decrease in overall crime, although murders and homicides had increased.

Duterte, nicknamed ‘the Punisher’, was voted to power promising to wipe out drugs and warning traffickers they risked death if they did not mend their ways.

The inquiry is being conducted by a staunch critic of the president, Senator Leila de Lima, who has summoned top police and anti-narcotics officials to explain the ‘unprecedented’ rise in the body count.

Duterte responded by warning legislators not to interfere with his campaign, saying they could be killed if they blocked efforts aimed at improving the country.

The United States, a close ally of the Philippines, said overnight it was ‘deeply concerned’ by the reports of the killings and the State Department urged Duterte's government to abide by human rights norms.

New York-based Human Rights Watch said the United States and European Union members ‘should make it clear to Duterte that inciting such violence is unacceptable and will reap potentially severe diplomatic and economic costs’.

‘Otherwise, it's hard to envision when these killings will end,’ it said.