MANILA, Philippines - A series of explosions signalled voting in Marawi City on Monday morning.

Police said a sport utility vehicle parked in front of an elementary school in Barangay Saduk exploded around 9 a.m.

Police Officer 3 Ali Rangirin, Saduk police investigator, said they have yet to determine the cause of the explosion.

Meanwhile, 3 successive explosions were heard near the Marawi State University before polling precincts opened at 7 a.m.

Initial reports said the explosions were caused by grenades.

The military said the groups responsible for the bombings are trying scaring voters to prevent them from casting their votes. -- Report from ronnie Enderes, ABS-CBN North Mindanao