The Office of the Prosecutor of the International Criminal Court (ICC) has welcomed the arrest and transfer of former president Rodrigo Duterte, describing it as an "important moment" for the victims of the alleged crimes committed during his bloody drug war.

In a video statement, ICC Prosecutor Karim A.A. Khan said that Duterte's arrest highlights that international law is not as weak as some may think.

"When we come together, when we work, when we build partnerships, the rule of law can prevail, warrants can be executed," he said.

"And the fact that it's been executed is important to victims. It means a lot, I think, to victims. That's the feedback we've already received," he added.

In a separate statement, the Office of the Prosecutor of the ICC said that Duterte's arrest was an important development in the Office’s pursuit of accountability in the situation in the Philippines for alleged crimes committed in the context of the drug war.

"This is a crucial step in our continuous work to ensure accountability for the victims of the most serious crimes under ICC jurisdiction," it said.

According to Khan, the Office of the Prosecutor was now preparing for the initial appearance and subsequent judicial proceedings before the ICC.

"It's important to underline, as we now start a new stage of proceedings, that Mr. Duterte is presumed innocent. He will make his initial appearance before the court soon," he said.

"The focus of the office is on the judicial proceedings, on improving its case before the judges of the International Criminal Court," he added.

Based on its independent and impartial investigations, the Office of the Prosecutor alleges that Duterte, as alleged founder and head of the Davao Death Squad, then Mayor of Davao City, and subsequently as the President of the Philippines, is criminally responsible for the crime against humanity of murder committed in the Philippines between Nov. 1, 2011 and March 16, 2019, before the country withdrew from the Rome Statute.

"Mr. Duterte is alleged to have committed these crimes as part of a widespread and systematic attack directed against the civilian population," the Office said in a statement.

"The Chamber also noted that the case against Mr. Duterte falls within the jurisdiction of the Court as the alleged crimes occurred during the period when the Philippines was a State Party to the Rome Statute, the ICC’s founding treaty," it added.

In the warrant of arrest issued on March 7, Pre-Trial Chamber I determined that there were reasonable grounds to believe that Duterte bore criminal responsibility for the crime against humanity of murder.

The Office of the Prosecutor then thanked the victims, survivors, witnesses, and activists from the Philippines who have cooperated with their investigation.

"Their strength, courage, and perseverance make these significant developments possible," it said, noting that those who still wish to cooperate may do so via its Witness Appeal portal.

The Office said its investigation in the situation in the Philippines continues and hopes to engage with the Philippine authorities on potential avenues of cooperation in pursuit of accountability.

"[The Office] will continue to rely on the partnership of national authorities, regional and international organisations, civil society, and the communities affected by Rome Statute crimes," it said.