Manila: More than 700 suspected drug users or dealers have been killed by police or vigilantes in the Philippines in less than three months, say human rights campaigners, who are calling on the UN to denounce the violence.

Human Rights Watch, Stop Aids and International HIV/Aids Alliance are among more than 300 civil society groups that have signed joint letters to the International Narcotics Control Board (INCB) and the UN Office on Drugs and Crime (UNODC), calling on them to break their silence over the crackdown.

“We are calling on the UN drug control bodies to publicly condemn these atrocities in the Philippines. This senseless killing cannot be justified as a drug control measure,” said Ann Fordham, executive director of the International Drug Policy Consortium (IDPC), which coordinated the letter.

Rodrigo Duterte, the president of the Philippines, won an electoral landslide in May after pledging to fill funeral parlous with drug dealers. He told Filipinos on the day of his inauguration last month: “If you know of any addicts, go ahead and kill them yourself as getting their parents to do it would be too painful.”

Since May 10 – the day Duterte was announced the winner of the presidential poll – at least 704 people have been killed because they were suspected to have been involved with drugs, according to monitoring by journalists at ABS CBN News, a Filipino news network.

One influential Philippine senator has called for an investigation into the killings. In a speech before the senate, Leila de Lima, a former justice minister, said: “We cannot wage the war against drugs with blood. We will only be trading drug addiction with another more malevolent kind of addiction. This is the compulsion for more killing.”

De Lima, who has also headed the Philippines’ national human rights body, said police were summarily killing even innocent people, using the anti-drugs campaign as an excuse.

A statement issued last week by the citizens’ council for human rights accused Duterte and his officials of abandoning due process and human rights in their zeal to fight the war on drugs. “Units of the Philippine national police, under the command of his close associate General Ronald “Bato” de la Rosa, have turned many low-income neighborhoods in the country into free-fire zones,” it said.

“The bloody encounters taking place daily have polarized the country between those who support the president’s quick and dirty methods of dealing with drugs and crime, and those who regard them as illegal, immoral, and self-defeating.”

The killings appear to have been carried out by police, who attribute the violence to suspects who “resisted arrest and shot at police officers”, and vigilante groups emboldened by Duterte’s promises of impunity.

In one case last month, eight suspected “drug personalities”, including a woman, were shot dead by police in a pre-dawn raid in the town of Matalam, about 900km (559 miles) south of Manila. On the same day in Manila, police said they found a man lying dead with his head wrapped in packaging tape and his torso covered with a cardboard sign reading: “I Am A Pusher.”

On another night in the capital, six people were killed by gunmen on motorcycles. One of the victims’ wives was photographed cradling his dead body in an image that has become emblematic of the Filipino drugs war.

Jennelyn Olaires, the wife of Michael Siaron whom police said was killed by a vigilante group, told Reuters her husband had not been a drug dealer but that he was addicted to drugs. She said the 29-year-old made money by riding a pedicab – a bicycle with a sidecar – and did odd jobs. He even voted for Duterte in the 9 May election.

“I don’t need the public’s sympathy. I don’t need the president to notice us,” Olaires said. “I know that he doesn’t like this kind of people. But for me, I just hope that they get the true offenders.”

The IDPC’s letters ask the UNODC and the INCB to call on Duterte to immediately end all his incitements to kill people suspected of dealing drugs and act to fulfil all international human rights obligations, including rights to life, health, due process and a fair trial.

Phelim Kine, deputy Asia director at Human Rights Watch, said: “International drug control agencies need to make clear to Philippines’ president Roderigo Duterte that the surge in killings of suspected drug dealers and users is not acceptable ‘crime control’, but instead a government failure to protect people’s most fundamental human rights.

“President Duterte should understand that passive or active government complicity with those killings would contradict his pledge to respect human rights and uphold the rule of law.”

A spokesman for the INCB said that a response to the IDPC’s open letter would be considered over the next few days. The UNODC said that it had received the letter and that it would be reviewed.

The most widely abused drugs in the Philippines are methamphetamine hydrochloride, known locally as shabu, and cannabis, which can easily be grown in the country’s rural areas. In 2014, 89% of drug seizures involved shabu while 8.9% involved cannabis, according to the Philippine Drug Enforcement Agency.

Before he was elected president, Duterte was a lawyer who earned a reputation as an authoritarian figure while he mayor of the southern city of Davao. His campaign pledges included the reintroduction of the death penalty by hanging, as well as offering bounties for the bodies of drug dealers.

During the campaign, Duterte said 100,000 people would die in his crackdown, with so many dead bodies dumped in Manila Bay that fish there would grow fat from feeding on them. After his election win, Duterte also launched a seemingly unprovoked attack against the UN.

“F*** you UN, you can’t even solve the Middle East carnage … couldn’t even lift a finger in Africa [with the] butchering [of] the black people. Shut up all of you,” he said.