MANILA- President Rodrigo Duterte’s threat to jail critics should they file an impeachment complaint against him was "righteous indignation," his spokesman said Friday.

Duterte on Thursday fumed over statements that he could be ousted if his pronouncement that Chinese fishermen can venture into Manila's waters became a policy.

"Hindi niya (Duterte) maintindihan, 'Ba’t hindi ninyo ako naiintindihan? Kayo na nga… ginagawa ko na nga iyong trabaho ko.' So in other words, it was a righteous indignation," Presidential Spokesman Salvador Panelo said.

(He can't understand why people don't understand him that he is only doing his work.)

• ‘Subukan niyo’: Duterte threatens to jail those planning to file impeachment case

Panelo explained that the President is simply after the welfare of all Filipinos.

“For so many weeks he has been holding his patience because he cannot understand why his critics, his detractors cannot understand that what he is doing is for the welfare, interest, and safety of our country,” Panelo said.

Former Foreign Affairs Secretary Albert Del Rosario earlier said that Duterte can be impeached for failing to defend the country’s territory, including its exclusive economic zone as mandated by the Constitution.

• Failure to defend national territory, including EEZ, basis for impeachment: Del Rosario

Opposition Senator Leila de Lima meanwhile said Duterte has committed betrayal of public trust, treason, and culpable violation of the constitution.

Contrary to the claims of the President's critics, Panelo said Duterte's actions are in line with his mandate to serve and protect the people.

“All the provisions of the Constitution emanate from that particular provision – that a primordial function of a government, the government which he heads now, is to serve and to protect the Filipino people,” he said.

Duterte earlier said Manila cannot drive Chinese fishermen away in the West Philippine Sea since Beijing also claims the area.

“We cannot drive them away, because they have insisted na kanila (that it's theirs too),” he said.

China claims nearly all of the South China Sea and has refused to recognize a United Nations backed-arbitral ruling that invalidated its sweeping claims in the vital waterway.