The Philippine government says its law enforcement agencies will be obliged to cooperate if the International Criminal Court seeks the custody of former President Rodrigo Duterte as part of an investigation into thousands of deaths during his crackdown on illegal drugs.

The Philippines said on Wednesday it would not stand in the way if former President Rodrigo Duterte wants to surrender to the International Criminal Court, and would be obliged to comply with any international arrest warrant over his "war on drugs".

President Ferdinand Marcos Jr said on Thursday his government would not block the International Criminal Court (ICC) if former leader Rodrigo Duterte wishes to be investigated over alleged crimes against humanity in his bloody anti-drugs crackdown.

Former Philippine President Rodrigo Duterte said the International Criminal Court (ICC) should 'hurry up' with its probe of his war on drugs, remaining firm in his defense of the brutal campaign as he said the investigation should start immediately.