The Philippines justice department on Monday labelled Vice President Sara Duterte the "mastermind" of a plot to assassinate the country's president, giving her five days to respond to a subpoena.
Duterte is being asked to explain herself in the wake of a blistering weekend press conference where she said she had instructed that President Ferdinand Marcos be killed should an alleged plot to kill her succeed.
"The government is taking action to protect our duly elected president," Justice Undersecretary Jesse Andres told reporters Monday.
"The premeditated plot to assassinate the president as declared by the self-confessed mastermind will now face legal consequences."
Hours earlier, in his first public comments on the matter, Marcos vowed to "fight back" in the face of a threat he labelled "disturbing".
The Marcos-Duterte alliance that swept to power in 2022 has collapsed spectacularly in the lead-up to next year's mid-term elections, with both sides trading allegations of drug addiction.
Duterte, who is facing potential impeachment hearings, told reporters early Saturday that she herself was the subject of an assassination plot and had instructed that Marcos be killed should it succeed.
In the expletive-laced press conference, Duterte also singled out first lady Liza Araneta-Marcos and presidential cousin Martin Romualdez as potential targets.
"I said, if I die, don't stop until you have killed them," she claimed to have told a security team member in regard to the trio.
Hours later, the presidential palace said it was treating the comments as an "active threat".
"That sort of criminal attempt must not go unchallenged," Marcos said Monday. "As a democratic country, we need to uphold the law."
"The vice president is not immune from suit. She can be the subject of any criminal or administrative case," Andres told reporters, adding the subpoena was in the process of being served.
He added that a manhunt was underway for the "assassin" allegedly engaged by Duterte.
- Marcos-Duterte rift -
Duterte, daughter of former president Rodrigo Duterte, was Marcos' running mate in the 2022 presidential election that saw their ticket win in a landslide.
She remains his constitutional successor should he be unable to finish his six-year term.
But she is currently facing an investigation in the House of Representatives, led by Romualdez.
Both Romualdez and Duterte are widely expected to run for president in 2028.
Duterte stepped down from her cabinet post of education secretary in June as relations between the two families reached breaking point.
Months earlier, her father had accused Marcos of being a "drug addict", with the president the next day claiming his predecessor's health was failing due to long-term use of the powerful opioid fentanyl.
Neither have provided any evidence for their allegations.
In October, Duterte said she felt "used" after teaming with Marcos for the 2022 poll.