MANILA - President Rodrigo Duterte has vowed to "destroy" an unnamed female government official after saying he has been a favorite whipping boy of rights groups and NGOs for the longest time.

"I have a special ano kay ano. She is a government official. One day soon I will - bitiwan ko yan (I will drop her) in public and I will have to destroy her in public," he told reporters.

Asked to provide clues, he said: "That is the riddle there, hintay lang kayo (just wait)."

He added that he is still waiting for a "go signal" to destroy the unnamed official.

The President also hinted that he had been "listening in" on another group with the help of another country.

"Akala nila hindi ako nakikikinig sa kanila (They think I am not listening to them) while all the time they have also been listening to what I have done. I have also been busy and with the help of another country listening to them."

"If you cannot catch me listening to you, then I will say there's nothing," he said.

Duterte has lashed out against several opponents in the past, criticizing former justice chief and now Senator Leila de Lima for trying to pin him to the killings of criminal suspects in Davao when he was still mayor.

He recently had a tiff with Chief Justice Maria Lourdes Sereno over his "name and shame" campaign against officials, including magistrates, who allegedly have links to narcotics.

The President later apologized to Sereno, saying he did not mean to issue harsh words.

Duterte apologizes to Sereno