MANILA, Philippines — Philippine authorities served him with a subpoena To Vice President Sara Duterte office on Tuesday, inviting her to answer questions from investigators after she publicly threatened to assassinate the president, his wife and the speaker of the House of Representatives if she herself was killed in an unspecified plot.

President Ferdinand Marcos Jr. Luni described her threat as a criminal plot and vowed to fight her and uphold the rule of law in the country in a looming showdown between the country’s two top leaders.

The national police and the military expressed alarm and immediately increased Marcos’ security. National Security Adviser Eduardo Ano said the threats are a matter of national security.

Duterte, a 46-year-old lawyer, said her remarks were not an actual threat but an expression of concern for her own safety due to the unspecified danger to her life. The Marcos administration’s statements against her were “a farce” and part of efforts to persecute critics like her, Duterte said.

The subpoena ordered Duterte to appear before the National Bureau of Investigation on Friday to “shed light on the investigation for alleged serious threats.”

Duterte said Monday she was willing to face an investigation, but asked the Marcos administration to also answer her questions, including alleged government irregularities.

Under Philippine law, such public remarks can constitute an offense of threatening harm to a person or their family and are punishable by imprisonment and a fine.

Marcos ran with Duterte as his vice presidential candidate in the 2022 elections and both achieved landslide victories to a campaign call for national unity. In the Philippines, the two offices are elected separately.

However, the two leaders and their camps soon fell out bitterly over key differences, including their approach to China’s aggressive territorial claims in the disputed South China Sea.

Duterte resigned from the Marcos Cabinet in June as education secretary and head of an anti-insurgency body and has become one of the most vocal critics of the president, his wife and his cousin Martin Romualdez, who heads the House of Representatives.

The House has been investigating Duterte’s alleged misuse of confidential government funds as Vice President and when she headed the Department of Education.