The former president of the Philippines, Rodrigo Duterte, will face trial at the international criminal court (ICC) after judges unanimously confirmed charges of crimes against humanity over his “war on drugs”.

Pre-trial judges concluded on Thursday that there were substantial grounds to believe Duterte was responsible for the crimes against humanity of murder and attempted murder in relation to anti-drugs crackdowns that led to the killing of thousands of people.

It is alleged that such crimes were committed as part of a “widespread and systematic attack” against the civilian population during Duterte’s presidency, which began in 2016, and his earlier term as mayor of the southern city of Davao.

Duterte, 80, who was arrested in Manila last year and flown to The Hague, has denied charges against him. The date of the trial has not yet been set. Rise Up for Life and for Rights, which represents families of the victims of drugs-related killings, said relatives were elated to hear the court decision.

“We have long waited for this moment. It’s been nearly 10 years since Duterte started implementing his deadly ‘war on drugs’. We look forward to seeing him in ICC court,” said Nanay Llore, whose sons were killed in May 2017.

Ritz Lee Santos, the director of Amnesty International in the Philippines, described the decision as a “historic moment for victims and international justice”.

It is not clear whether Duterte will attend the trial. He did not appear at pre-trial hearings in February, which were held to determine the merits of the case, saying in a statement at the time that he was “old, tired and frail” and experiencing memory loss.

Duterte’s defence team have argued that he is unfit to stand trial because of apparent cognitive decline. His lawyers also challenged the case by arguing the court did not have jurisdiction, a claim that was rejected.

The prosecution has accused Duterte of being “at the very heart” of brutal anti-drugs campaigns launched during his time as mayor of Davao and as president. In the February hearings, it was argued that the former leader wielded “ultimate influence and authority” over the perpetrators of drug crackdowns, authorising murder, selecting some of the targets, promising immunity and giving financial support to perpetrators.

“He ran a death squad in Davao that he created. He ran it for over 20 years before he became president. His promise was to kill thousands and he did,” said Julian Nicholls, summing up for the prosecution after the hearings.

The prosecution quoted from several of Duterte’s speeches that appeared to incite or confess to violence. Duterte was quoted as saying in a television interview: “If I become president, you will all get wiped out. I will order your execution within 24 hours.”

As many as 30,000 civilians were killed in connection with drug operations, according to past estimates cited by the ICC prosecutor. Many were men in poor, urban areas who were shot dead in the streets or in their homes. Philippine national police have reported more than 6,000 deaths related to anti-drugs operations.

Duterte’s defence lawyer, Nicholas Kaufman, said in February that Duterte’s speeches were full of “hyperbole, bluster and rhetoric”, but he should not be judged based on his “vulgar language”.

In a statement to AFP on Thursday, Kaufman said the idea that people were killed as a “state policy” would be proved a “complete fiction” during trial.

“The defence will also show that the evidence of … criminal witnesses, so gleefully peddled by the former president’s many detractors, has zero weight,” he said.