MANILA, Jan 13 (AFP) - The chief suspect in the Philippines' worst political massacre personally led the cold-blooded ambush and murder of 57 people including pregnant women, the star prosecution witness said Wednesday.

Andal Ampatuan Jnr has pleaded not guilty to multiple counts of murder over the November attack on a political rival's convoy in the southern province of Maguindanao where the victims were abducted, shot and buried in mass graves.

But in the first graphic evidence since the trial began last week, the deputy mayor of a town in the province said he witnessed first hand the scenes of carnage and said Ampatuan himself pulled the trigger against three victims.

Rasul Sangki, the deputy mayor of the town of Ampatuan, told the court he saw relatives and supporters of Ampatuan Jnr's political rival Esmael Mangudadatu being hauled away at gunpoint after their convoy was ambushed on November 23.

"The people were afraid. There were people pleading with them. They were pushed, struck, dragged by the people of Datu Unsay," Sangki said, referring to Ampatuan Jnr by his nickname.

"I saw Datu Unsay shoot (journalist) Jimmy Palak and two women. Before they were shot, they were pleading. The women were screaming," he said.

"He shot them, even the ones who were already dead," he added.

Ampatuan Jnr, a town mayor and scion of one of the country's most powerful Muslim clans, was in the dock for the second hearing in the trial after being taken in handcuffs to a special courtroom at national police headquarters.

Sangki said Ampatuan had even informed him four days before the massacre of a plan to block the convoy as Mangudadatu's supporters travelled to register him as a candidate to run against Ampatuan in the race to become Maguindanao governor in May elections.

"I did not know what was going to happen," insisted Sangki, who said he was taken by Ampatuan to the site of the ambush but that he himself had no part in the shootings.

A total of 57 people were killed, including pregnant women and at least 30 journalists in the attack that stunned the nation and raised questions about the influence of the Ampatuan clan in President Gloria Arroyo's government.

During the car ride to the massacre site, Sangki said the defendant spoke by radio to a person he recognised as Ampatuan's father and clan leader Andal Ampatuan Snr, who is the current Maguindanao governor.

Ampatuan Jnr, who was being groomed to succeed his father, said "father, they are here already," to which Ampatuan Snr replied, "you know what to do already," Sangki said.

Sangki said the defendant's uncle as well as other gunmen fired repeatedly on the victims' bodies even after they had fallen to the ground to make sure there were no survivors.

Ampatuan Jnr's lawyer sought to discredit Sangki by demanding why he had failed to report the killings to the authorities.

"I have no faith in the law. The PNP (Philippine National Police) and the military belong to them (the Ampatuans)," Sangki said.

He said Ampatuan Jnr also warned him after the massacre to "tell your people they did not see or hear anything."

Sangki was brought in to testify by the prosecution, which is trying to block Ampatuan Jnr's bail application. The trial continues next week.

Ampatuan Snr and several other clan members were also arrested after martial law was briefly imposed in Maguindanao and charged with rebellion. No date for their court appearance has been set.

Critics say Arroyo cultivated ties with the Ampatuan clan and provided them firepower to contain Muslim separatist rebels in the southern Philippines. (By Mynardo Macaraig/ AFP)