MANILA - The Office of the Ombudsman reiterated its constitutional duty as President Rodrigo Duterte issued another tirade amid a probe into his and his family's wealth.

"The Ombudsman has already stated its position; to abide by its constitutional duty. No need to add more," the Office of the Ombudsman said in a tweet Sunday.

This was a response to Duterte's dare to both Ombudsman Conchita Carpio Morales and Supreme Court Chief Justice Maria Lourdes Sereno to resign amid the investigation.

The President hit the Ombudsman anew for allegedly administering "selective justice" in prioritizing the corruption investigation against him.

"Morales, unahin mo iyung mga kaso nun na nai-file matagal na. You are on a selective justice. ******. Bakit nauna iyang sa amin na hindi pa totoo?" he said.

The Ombudsman has already stated its position; to abide by its constitutional duty. No need to add more.

— OmbudsmanPH (@OmbudsmanPh) October 1, 2017

Overall Deputy Ombudsman Arthur Carandang last week said his office had obtained from the Anti-Money Laundering Council (AMLC) bank transaction documents of the Duterte family in line with its probe.

Carandang said the family’s transactions amount to hundreds of millions of pesos from different banks between 2006 until 2016. But Duterte said these are "falsified" documents.

The President said AMLC itself denied releasing information to the Ombumdsman.

Morales earlier said the Ombudsman is "not intimidated" by the President's announcement that he will form a commission to investigate the government office.

• READ: Unfazed, Ombudsman to pursue probe of Duterte family's wealth

"Sorry, Mr. President but this office shall not be intimidated," Morales said in a statement.

"The President's announcement that he intends to form a commission to investigate the Ombudsman appears to be a retaliation to our ongoing investigation. We will, nonetheless, proceed with the probe, as mandated by the Constitution," Morales said.