MANILA -- A sub-leader of the Maute group that laid siege to the southern city of Marawi in 2017 has surrendered to authorities in Lanao del Sur, the military said Thursday.

With the surrender of Hilal Biston alias Pakistan on Wednesday, the military hopes more members the group will turn themselves in, said Col. Romeo Brawner, commander of the military's 103rd Infantry Brigade.

Biston fought military troops in neighboring Piagapo and Butig townsb before the 5-month siege that destroyed large swaths of Marawi, said Brawner.

Some Maute fighters have surrendered in the last 2 years, but the military remains on alert against possible Maute attacks, he said.

Marawi and the towns of Marantao, Bacolod Kalawi and Malabang, were earlier deemed as the most critical areas in Lanao Del Sur for Monday's elections, where additional troops will be deployed.