Duterte insisted he would not be intimidated by criticism of the drug war, which rights groups have said could be a crime against humanity.
"Don't trust those human rights (critics), if you do I will cut off both your heads," Duterte said in a speech to inaugurate a bridge in the southern Philippines.
"I will not be influenced by any fear. Jail me. So jail me. If they say I should be jailed, okay. Fine. I'll pay the price."
"Make that 50,000. I will really finish them off. And even if I go to hell, I can rot in prison. I do not mind. I am old."
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Duterte's comments came shortly after his spokesman said the Philippines would refuse European Union grants that "interfered" with its internal affairs.
The European Union has been one of the most vocal international critics of the drug war.
Abella said one grant had already been declined for having "objectionable" conditions attached to it, although he refused to elaborate.
The European Union is the Philippines' eighth biggest source of aid, with assistance last year worth USD 217 million, according to government data.
Much of the aid is spent on projects to help end Muslim and communist insurgencies in the southern Philippines.
It was not clear how much money was in jeopardy.
Economic secretary Ernesto Pernia added to the confusion by saying the announcement of rejecting aid may just be a response by Duterte to the criticism and he may retract it.
Duterte, 72, has repeatedly criticised European lawmakers and the EU for condemning his drug war.
The European Union has said it is reviewing Philippine exports' duty-free status because of rights concerns, which also include Duterte's plans to bring back the death penalty and lower the age of criminal responsibility to nine.
The German government also expressed concern after Duterte last year drew parallels between his drug war and the Holocaust perpetrated by Adolf Hitler's Nazi Germany.
"Hitler massacred three million Jews. Now there are three million drug addicts (in the Philippines). I'd be happy to slaughter them," Duterte said, underestimating the number of people killed in the Holocaust.
Duterte later apologised for the Hitler reference but said he was "emphatic" about wanting to kill addicts.
Duterte easily won presidential elections last year after promising to end crime by killing tens of thousands of drug traffickers and addicts.
Unknown assailants have killed more than 1,800 others, while about 5,700 other violent deaths are under investigation, according to police data.
Partly in response to American criticism of the drug war, Duterte has also loosened the Philippines' ties with traditional ally the United States.
Duterte has instead embraced China, which has supported his drug war and sought to deepen economic ties by providing billions of dollars worth of investments and aid to the Philippines.