Andal Ampatuan Jr. surrendered to police in General Santos City, Philippines, after charges were laid against him in connection with the massacre of 57 people in November. (Associated Press)

A member of a powerful family in the Philippines accused of orchestrating the massacre of 57 people, including journalists and family members of a political rival, pleaded not guilty Tuesday on the first day of his trial in Manila.

Andal Ampatuan Jr., a town mayor in the province of Maguindanao on the country's southern island of Mindanao, was charged with 41 counts of murder in the Nov. 23 attack on an election caravan.

Among those killed were at least 30 journalists and their staff, in what is considered the world's deadliest single attack on media workers.

Prosecutors said they have witnesses who will testify that Ampatuan led more than 100 armed militiamen and police to stop the election caravan of Ismael Mangudadatu, vice-mayor of Buluan township.

The caravan was on its way to register Mangudadatu as a candidate for provincial governor in Maguindanao, for which he would be competing against Ampatuan's father, Datu Andal Ampatuan Sr.

It is alleged the caravan members, including Mangudadatu's wife and sisters but not the candidate himself, were then escorted to a hilltop clearing and gunned down or hacked to death and then buried in mass graves.

Mangudadatu had sent his family to register him in his stead after he received death threats. But he believed his family members would be safe.

Martial law imposed after attack

The killings sparked international outrage and led Philippines President Gloria Macapagal Arroyo to briefly impose martial law in Maguindanao to crack down on the Ampatuan clan and its militia.

The Ampatuan family had been close allies of the president, delivering crucial votes to Arroyo and her circle in the 2004 presidential and 2007 senatorial elections.

Arroyo also expelled both father and son from her ruling Lakas Kampi CMD party, as well as another son, Zaldy, governor of the nearby Autonomous Region in Muslim Mindanao.

Neither the elder Ampatuan nor Zaldy has been indicted in the killings. They have also denied any role in the massacre.

The southern Philippines region has a history of election-related violence due to the presence of armed groups. Muslim insurgents have been waging a campaign since the 1970s, while some politicians maintain private militias. But the scale of atrocity in the November massacre was shocking, even by the standards of the often lawless province.

The trial is set to resume Jan. 13, when Ampatuan's lawyer Sigfrid Fortun said he would ask for his client to be released on bail.

With files from The Associated Press