MANILA - The Commission on Elections said it was investigating whether an explosion at the house of a judge in Cotabato City was connected to Monday's plebiscite for the ratification of the Bangsamoro Organic Law.

A hand grenade exploded outside the house of Judge Rosalito Rasalan on Sunday night. Another explosive was lobbed in the roof, but did not explode. No one was hurt in the incident.

Rasalan is a critic of the BOL, which if ratified would create the Bangsamoro region where the Muslim minority would have wider self-rule, noted Comelec.

The judge's brother is also a secretary of the mayor of Cotabato City, whose residents will vote on whether or not they want to be part of the new region, added the poll body.

The Comelec said it was also investigating whether the blast was connected to Rasalan's job as a judge of Maguindanao's Municipal Circuit Trial Court.

The explosion came about 2 weeks after a New Year's Eve bombing outside a mall in Cotabato City, which left 2 dead at least 34 injured.

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Military choppers with high-vision capability patrolled over the southern metropolis early Monday.

Some 20,000 soldiers and policemen were deployed to Cotabato City, Isabela City in Basilan and the ARMM region for the Bangsamoro plebiscite.

President Rodrigo Duterte, who hails from Mindanao's Davao City, has banked on the measure to correct "historical injustices" against the Moros.

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Moro groups' struggle for self-governance has claimed an estimated 150,000 lives, although most of the deaths occurred in the 1970s. Ceasefires put in place for the past decade to allow peace talks have largely held.

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With reports from Dexter Ganibe, ABS-CBN News; Agence Fracne-Presse