“The manner of executions reflects the killings made here in Metro Manila, the difference being the drug operations are committed in another area with new victims,” she said.

“This past year, various news reports show that while Metro Manila has registered a reduction [in] the number of deaths in their drug-related operations, nearby provinces and regions have recorded more than one death a day, specifically Central Luzon, and that it has become the new focus of the war on drugs.”

De Lima said she wanted to know if police officers were using the drug war to justify human rights abuses and other unlawful acts.

“It is also imperative to look into the factual and legal issues relating to these killings and determine whether these killings were products of legitimate police operations, the rights of suspects or persons subject of operations have been observed, and existing procedures on seizure and arrest have been complied with,” she said.

Colonel Bernard Banac, spokesman for the Philippine National Police, said that they would welcome any investigation, but attributed the increase in deaths in Central Luzon to drug lords and protectors “liquidating” their own people.

“The case of Central Luzon is not conclusive. It still needs validation because there were many cases of homicide that need to be investigated, if they were drug related, as well as the circumstances surrounding the deaths,” he said, citing a recent case where five suspected drug traffickers were found dead in a safe house in San Jose del Monte, north of Manila.

“Our figures have increased because the suspects were putting up strong resistance. Although if we can look closely, there was less incidence compared to the early stages of our campaign.”

According to official police statistics, about 5,300 people have been killed in the country’s war on drugs since 2016 - up from 5,000 deaths until December.

But rights groups put the figure at between 20,000 and 30,000, saying that thousands of deaths attributed to pro-government vigilantes have been unaccounted for.

How Philippines war on drugs has become a war on the poor

Carlos Conde, Philippines researcher for Human Rights Watch’s Asia Division, said the deaths will continue unless international organisations, such as the UN Human Rights Council and International Criminal Court, intervene.

“The Duterte administration is determined to pursue the ‘drug war’ because it serves a political purpose … regardless of the fact that it is not working to eliminate illegal drugs in the country.”

Human Rights Watch has called on the International Criminal Court to speed up its investigation, launched early last year, into the extrajudicial killings carried out as part of Duterte’s anti-drugs campaign.

The court is currently considering two complaints that have been made against the Philippine president: one filed by a former policeman and self-styled assassin who alleged that Duterte ordered the killings of criminals and opponents while mayor of southern Davao city; and a second filed by the relatives of eight people killed in the drug war.

In a speech to the upper chamber on Wednesday, Senator Panfilo Lacson, a former national police chief, blamed massive corruption at the Bureau of Customs for the proliferation of drugs in the country.

“We spend a great deal of taxpayers’ money for an automated processing system, X-ray scanners, even for brokers’ accreditation, not to mention fairly high salaries for seasoned military men at the helm of the Bureau of Customs. But at the end of the day – all our efforts be damned – we are still in one hell of a mess,” he said.

“Illegal drugs, the worst kind of toxic goods that reek of evil and leave pernicious effects on at least a million souls in our society today, have also found their way into this benighted land.”

In Philippines, Duterte’s drug war finds a new target: 9-year-olds

The senator cited the case of Chinese national Zhijian Xu, also known as Jacky Co, who stands accused of helping smuggle millions of dollars worth of crystal meth into the port of Manila, which authorities seized two months ago.

He said that Xu was allowed to enter and leave the country despite being on an Interpol watch list.

“In spite of his alleged involvement in criminal activities here and in China, he left Manila via a Philippine Airlines flight bound for Vietnam,” Lacson said.

“One may wonder: How can a person of such character slip [through] the stringent scrutiny of the Bureau of Immigration personnel manning our airports considering that [they] now use ‘state-of-the-art, biometrics-based system for [their] computers in all international airports nationwide?’”