MANILA, Philippines — A powerful Filipino clan leader who is a suspect in the 2009 massacre of 57 people pleaded not guilty Monday to charges of rigging elections to favor former President Gloria Macapagal Arroyo's allies.

Andal Ampatuan Sr., who is currently on trial for murder in the massacre, was separately arraigned on the charge of electoral sabotage. Arroyo, his former political patron, has pleaded not guilty to the same electoral charge. She has not been linked to the massacre.

The court also entered a not guilty plea for former Philippine elections chief Benjamin Abalos, who questioned the court's jurisdiction and refused to enter a plea himself.

One of the most feared politicians in the country, Ampatuan, his three sons and more than 150 gunmen are accused of killing at least 57 people, including 32 journalists, who traveled in a convoy to register the candidacy of a political rival of the Ampatuans.

The ambush in southern Maguindanao province, the Ampatuans' bailiwick where clan members held several positions, including governor and mayor of several towns named after them, was the worst political massacre in recent Philippine history and the worst single killing of journalists in the world.

Ampatuan and the other accused have pleaded not guilty to murder charges.

Ampatuan, the 70-year-old clan patriarch, was brought to court from his detention cell in a wheelchair Monday by heavily armed police. His arraignment had been postponed twice because he was treated for pneumonia in a military hospital early this month.

The main witness in the electoral sabotage case is Norie Unas, a former provincial administrator, who says he overheard Arroyo instruct Ampatuan to ensure a victory in the 2007 congressional election for all 12 senatorial candidates allied with her.

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Not a single opposition candidate won that year in Maguindanao, and years later the election tribunal found evidence of vote tempering.

Meanwhile, a grandson of Ampatuan — one of nearly 100 massacre suspects at large — was turned in by his mother and taken into custody.

Anwar Ampatuan Jr.'s mother, who is a town mayor, feared for her son's life after he was hurt in a bomb blast Sunday, said military Col. Mayoralgo dela Cruz. It was not clear who was behind the blast.

The massacre victims' relatives have criticized the slow pace of the trial, which opened in Manila in 2010.