MANILA, Philippines -  The National Bureau of Investigation on Friday said it will go on heightened alert throughout the weekend over an alleged terrorist plot to bomb the NBI and Supreme Court on January 31, Sunday.

Ric Diaz, NBI spokesman and counter-terrorism unit head, said the January 31 bomb threat is connected to the discovery of an improvised explosive device in Greenhills Shopping Center in San Juan last January 26. Authorities said the explosive was found near a map detailing the NBI headquarters and Supreme Court offices on Taft Avenue.

Diaz said the bomb threat could be a scare tactic to transfer Datu Unsay Mayor Andal Ampatuan Jr. to a different facility in the hopes of rescuing him. Ampatuan is the prime suspect in the election-related massacre of 57 people in Maguindanao province last November 23.

The NBI spokesman said state witnesses have also received mounting pressure to dissuade them from testifying. Last week, an alleged cousin of Ampatuan Vice-Mayor Rasul Sangki was murdered while the house of another witness, Noh Akil, was torched.