Acosta confirmed the report in a telephone interview with MindaNews Wednesday.
He said the grenade was lobbed from behind the rally's crowd in a covered court in Dagumba-an village, around 10 kilometers west of Maramag town proper.
Dagumba-an is near Brgy. San Miguel where Valle Escondida, the residence of Acosta's only opponent, reelectionist Gov. Jose Ma. R. Zubiri is located.
The grenade hit a tree before exploding at least 10 meters away from where he was speaking, Acosta said.
Acosta described the explosion as a "big blast." He said no one was hurt in the incident and the campaign party's vehicles parked nearby were spared.
He said the blast interrupted him in the middle of his speech trying to expose the alleged anomalies of the Zubiri administration.
He said he then asked the audience if they would allow harassments such as the incident to stop them from knowing the truth.
The Acosta camp said they pushed through with the rally despite the incident.
Acosta said they have already filed a police blotter of the incident but the assailant has remained at large.
Acosta alleged that it was thrown by someone from the camp of Zubiri, who he claimed got angry that he campaigned in his turf.
Zubiri has denied harassing the Acosta campaign and earlier, even ordered police investigation of incidents decried by the latter as "political harassments."
He told ANC Wednesday afternoon that the explosion could have been the handiwork of Acosta’s camp to get sympathy votes. He also asked how Acosta came to the conclusion it was a grenade that exploded.
Fr. Danilo Paciente, Namfrel provincial coordinator and concurrent head of the Parish Pastoral Council for Responsible Voting (PPCRV) in the province, said any form of violence is no good for the election but they have to probe the incident as the two camps have opposing reports.
Paciente said Zubiri in an interview with DXDB denied involvement and claimed the blast was 60, not 10 meters away from Acosta. Paciente said they will await the investigation before making a statement.
Acosta said the incident has prompted their camp to take extra precautions and be more careful of security considerations. It was the sixth rally they held in Maramag, Acosta said.
Acosta is finishing his last term as representative of the first congressional district in Northern Bukidnon. Zubiri, from the south, is running for his last term as governor.
Acosta blocked an earlier proposal by Zubiri’s son, Juan Miguel, who is now running for senator, to divide the province of Bukidnon into two.
The Acostas and the Zubiris are the two biggest families in Bukidnon politics, with three Acostas and four Zubiris in the campaign for the May 14 polls.
Acosta’s sister, Malou, is running for the post her brother will vacate while his mother is seeking reelection as mayor of Manolo Fortich town, the center of the first district.
Aside from Gov. Zubiri and Rep. Zubiri, Jose Ma. Zubiri III is eyeing the senatorial bet's post as third district representative. The governor's nephew, Iñaki is seeking reelection as Malaybalay City vice mayor. (Walter I. Balane/MindaNews)