Philippine President Benigno Aquino warned Sunday that authorities have discovered a plot by a terrorist group to disrupt a huge religious procession in Manila.

Mr. Aquino did not identify the group, but said at a news conference that several terrorists had been spotted in the capital city, and that police are attempting to detain the suspects and disrupt any planned attack.

The Philippine leader said security will be very tight for the procession Monday of a centuries-old wooden sculpture of Jesus known as the Black Nazarene. The annual festival draws hundreds of thousands of spectators.