The accused sit at the trial venue inside a prison facility at Camp Bagong Diwa, Taguig City, Philippines. Picture: Supreme Court - Public Information Office via AP

Manila - A Philippine court on Thursday convicted several members of an influential political clan in the country on 57 counts of murder in the country's worst election-related killing that took place 10 years ago.

Judge Jocelyn Solis Reyes sentenced 28 suspects found "to have acted as principal" in the massacre, including Andal Ampatuan Jr, his brother Zaldy and six other relatives, to life imprisonment or 40 years in jail without parole.

Fifteen defendants were convicted as accomplices to the killing and sentenced to at least six years in prison, while more than 50 other accused were acquitted, including four members of the Ampatuan family.

The November 23, 2009, massacre in a remote, hilly village in Maguindanao province, 960 kilometres south of Manila, sparked local and international outrage and highlighted the culture of impunity in the country.

Fifty-eight people were killed in the massacre, but the convictions were only for 57 murders because the body of the last victim has not yet been found. 

House representative Esmael Mangudadatu, whose wife and relatives were one of the victims in a 2009 election-related killings, gestures as he steps out the court inside a prison jail at Camp Bagong Diwa, suburban Taguig, Metro Manila, Philippines. Picture: Aaron Favila/AP

The Ampatuan clan, which ruled Maguindanao for decades, allegedly planned the attack months before to prevent a rival from challenging their control in elections in May 2010.

The victims included 20 relatives, lawyers and supporters of then town mayor Esmael Mangudadatu, who were travelling in a convoy to file his certificate of candidacy for provincial governor in the 2010 elections.

They were accompanied by 32 journalists and media workers, as the candidacy was considered big news in the province and the country as the Ampatuans often ran unchallenged in elections.

Mangudadatu, who is now congressman, hailed the convictions, despite admitting he felt a little disappointed that some of the Ampatuan family members were acquitted.

"We are thankful to Judge Reyes that the major suspects were found guilty," he said. "That was our prayer."

"They have shown no remorse," he told reporters earlier before the verdict was read, referring to the Ampatuan family. "They should be punished."

The victims also included six civilians who were passing by the area where Andal Jr and armed men stopped the convoy at a police checkpoint along the highway, led the vehicles to a slope away from the road where they were gunned down.

The suspects also tried to bury the bodies and their vehicles, using a backhoe owned by the local government.

Human rights and press freedom groups said the verdict was not the end of the fight for justice.

"This momentous verdict should help provide justice to the families of the victims, and build toward greater accountability for rights abuses in the country," said Phil Robertson, deputy Asia director for Human Rights Watch.

"Advocates should use this verdict to spur further political and judicial reforms to ultimately end the impunity that has plagued the country for far too long," he added.

"More broadly, this verdict should prompt the country's political leaders to finally act to end state support for 'private armies' and militias that promotes the political warlordism that gave rise to the Ampatuans."

Security was tight at the police camp where the verdict was read, in a proceeding allowed by the Supreme Court to be broadcast live nationwide.

Heavily armed anti-riot policemen guarded the entrance to Camp Bagong Diwa, while snipers were seen on the roof. Dozens of protesters gathered outside, with placards reading "Convict Ampatuans," "Justice Now" and "End Impunity."