Unidentified persons lobbed a hand grenade at a house of a local judge in Cotabato City in the southern Philippines on Sunday, the eve of a plebiscite to ratify a law that will establish a larger Muslim autonomous region in Mindanao.

Police Chief Inspector Efren Salazar, commander of a city police station, told reporters that the incident happened shortly after 9:00 p.m. on Sunday at a village in front of the house of Judge Rosalito Rasalan.

Quoting witnesses, Salazar said the grenade landed on the roof but rolled down and exploded on the ground.

No one was injured in the explosion, he added.

Salazar said an investigation is underway. He said it is not conclusive if the attack was related to the plebiscite scheduled for Monday.

No group has claimed responsibility for the attack.

The attack took place amid tight security in the region. Authorities said at least 10,000 soldiers and policemen have been deployed to ensure the voting will be orderly and peaceful.

The Commission on Elections of the Philippines said a total of 2.8 million voters registered for the plebiscite to decide whether to ratify the landmark Bangsamoro Organic Law (BOL), which is expected to pave the way for wider self-rule to the Muslim minority in the Philippines and is hoped to end the decades-old conflict in the region.

If the BOL is ratified, a Bangsamoro Autonomous Region in Muslim Mindanao will be created and the region will enjoy more political and economic power, including greater fiscal autonomy, a regional government, parliament and justice system.

The Philippine government hopes the BOL can pave the way for the integration process of the thousands of former separatist rebels and their families to reintegrate into mainstream society and live peaceful and productive lives.