The family of Senator Risa Hontiveros has also been receiving death threats, National Bureau of Investigation (NBI) Director Melvin Matibag said on Monday.

Matibag disclosed that the NBI has already identified persons of interest as part of its ongoing investigation into the threats.

According to the NBI chief, investigators have made progress in the probe but declined to disclose further details to avoid compromising the investigation.

"Meron, actually na-penetrate na namin. I cannot give so much details because we are investigating it," Matibag said when asked whether Hontiveros' family had also been targeted.

Asked if the bureau had already identified persons of interest, Matibag replied: "Yes."

The development comes as the NBI continues its investigation into hundreds of social media posts allegedly threatening Hontiveros following the killing of pro-administration vlogger Alicia Lipata, popularly known as Mima Alicia.

The office of Hontiveros earlier sought the NBI's assistance after submitting the names of hundreds of Facebook users and screenshots of posts allegedly containing death threats against the senator.

The NBI previously said its Forensic Laboratory and Cybercrime Division would conduct forensic examinations and digital analyses of the identified accounts as part of its case build-up to determine whether criminal charges should be filed before the Department of Justice (DOJ).