The Philippines' security council will verify an alleged assassination threat by Vice President Sara Duterte against President Ferdinand Marcos Jr., a top official said on Sunday, describing it as a "matter of national security."

Duterte, in a strongly-worded morning briefing on Saturday, said she had spoken with an assassin and instructed them to kill Marcos, his wife and the speaker of the Philippine House if she were to be killed.

National Security Adviser Eduardo Ano said the government considers all threats to the president as "serious," vowing to closely work with law enforcement and intelligence communities to investigate the threat and possible perpetrators.

"Any and all threats against the life of the president shall be validated and considered a matter of national security," Ano said in a statement.

The Presidential Communications Office, citing the justice ministry, said Duterte's threats are now under investigation and may lead to charges.

"If the evidence warrants, this could lead to eventual prosecution," Marcos' office said in a statement.

Duterte's threat stemmed from an order by lawmakers to transfer her chief-of-staff to a jail for allegedly impeding its probe over the vice-president's alleged misuse of public funds.

In response to Duterte's threat, Marcos' presidential security command said it had tightened its protocols in guarding the Philippine leader and the national police chief had ordered an investigation.

Duterte, the daughter of former President Rodrigo Duterte, and Marcos were once political partners who won an overwhelming mandate to lead the nation's top two offices in 2022. The alliance crumbled this year over policy differences, including foreign policy and the elder Duterte's deadly war on drugs.

Marcos' congressional allies are separately investigating Rodrigo Duterte's campaign that led to more than 6,000 killed in anti-drug operations and alleged corruption over Sara Duterte's use of public funds during her tenure as education secretary. Both have denied wrongdoing. Duterte quit her Cabinet post in June.