(CNN) US Secretary of State Nominee Rex Tillerson says that the country will preserve its "longstanding friendship" with the Philippines, despite the violent anti-drug campaign of leader Rodrigo Duterte.

During Tillerson's Senate Foreign Relations Committee confirmation hearing on Wednesday, Senator Marco Rubio asked Tillerson whether the killings in the Philippines were "conducive to human rights violations that we should be concerned about and condemning."

Tillerson said he'd need further "facts from the ground" before commenting.

Since Duterte took power in June, he's waged a bloody so-called "war on drugs," in which he's encouraged police and vigilantes to shoot drug dealers and users.

More than 6,000 people have been killed, including a six-year-old Manila boy who was shot in his sleep last month.