MANILA The Philippines has said its investigation into killings during former President Rodrigo Duterte's war on drugs will be "impartial", a day after its attempt to block a similar probe by the International Criminal Court (ICC) was rejected.

Amid criticism from victims' families and rights groups over a lack of accountability, the Department of Justice (DOJ) said on Wednesday it would "ensure a fair and impartial investigation into any allegations of human rights violations or abuses".

Thousands of people were killed during anti-drug operations that ended in shootouts during Duterte's term, rights groups say. Police have officially acknowledged roughly 6,200 deaths and reject accusations of systematic executions and cover-ups.

"We understand the importance of providing a platform for victims to be heard, and we assure everyone that their voices will be listened to and taken seriously," the DOJ said in a statement.

"Our goal is to provide justice and accountability while upholding the rule of law," it added.

On Tuesday, ICC appeal judges rejected the Philippines' attempt to block a probe into the thousands of drug war killings in the country, saying it was unconvinced Manila was conducting relevant investigations.

The ICC is a court of last resort to prosecute individuals for atrocities when a state is unwilling or unable to do so.

The DOJ maintains the country's legal system is functioning well and it encouraged individuals with evidence and witnesses to come forward.

Among those killed in the war on drugs was high-school student Kian delos Santos, whose death in 2017 led to the first convictions of police officers in the drugs war, and was featured in a report by a former ICC prosecutor.

The Philippines in 2021 reviewed drugs war cases that indicated foul play in dozens of deadly police operations, marking a rare admission by the state that abuses may have taken place.

(Reporting by Neil Jerome Morales; Editing by Kanupriya Kapoor)