President Rodrigo Duterte has vowed to have the 84-year old mother of opposition Senator Antonio Trillanes IV subpoenaed over alleged anomalous transactions that she entered into with the Philippine Navy decades ago.

"We will initiate an investigation just like yours and I will subpoena your mother whether you like it or not," Duterte said in a speech during the 2019 General Assembly of the League of Municipalities of the Philippines at the Manila Hotel Tuesday night.

Duterte said he has the power to call Trillanes' mother during the investigation.

"We also have the contempt power but we have to go to court," he added.

In his previous speeches, Duterte accused Trillanes' mother Estelita of being a supplier for the Philippine Navy even if her husband was a Navy officer. He has accused of possible conflict of interest.

In a statement on Wednesday, Trillanes dared Duterte to do his threat to subpoena her mother.

"Since September last year, Duterte has been saying that he asked different agencies to investigate the supposed anomalous transactions of my Mother. But up to now, he has yet to show even a shred of evidence to prove his baseless allegations," he said.

"Now, Duterte is threatening to subpoena my Mother. Just do it and let it be another humiliating episode for you like the fake offshore bank account you alleged against me," Trillanes stressed.

Since Duterte could not break him, he said even his ailing mother is being dragged into the issue.

"It's okay, do your worst while I count the days," he added.

Trillanes, a staunch critic of the President, was behind the complaint against Duterte before the International Criminal Court for alleged crimes against humanity due to the administration's bloody war on drugs. Celerina Monte/DMS