MANILA, Philippines?A grenade explosion killed three people and wounded 50 others Wednesday after police said they thwarted two possible terrorist attacks, including one that may have targeted President Gloria Macapagal Arroyo.

The grenade blast occurred around 9:45 p.m., while people were dancing on a basketball court that had been turned into a trade fair during May Day celebrations at Notre Dame village, part of Cotabato city.

Col. Essel Soriano, the local military commander, said it appeared that someone lobbed the grenade and ran.

Earlier, two large pipe bombs and a map of Davao city?which Arroyo visited a few hours later?were found in a raid on a house about an hour’s drive away. The map had markings that police said might have indicated attack targets. Also confiscated were two pistols, a grenade and bomb-making gear.

Police arrested three suspects.