A Philippine politician was charged with mass murder on Friday after authorities accused him of ordering soldiers, police and other gunmen to kill at least 57 defenceless people in an organised slaughter.

Andal Ampatuan Jnr, a mayor in the lawless southern Philippines who until this week was an ally of President Gloria Arroyo, was charged with seven counts of murder, the government said.

"He was the one who gave the instructions. He was among those ... who killed the victims," Justice Secretary Agnes Devanadera told reporters as she outlined the case against Ampatuan Jnr.

Devanadera also announced the suspect's father, the leader of the Ampatuan clan and governor of Maguindanao province, was among eight other members of the powerful family under investigation and not allowed to leave the country.

An emotional Devanadera earlier on Friday gave the most detailed official account yet of Monday's election-linked massacre, saying the female victims may have also been raped.