MANILA - The Philippines have charged 196 more people with murder over a pre-election massacre in Maguindanao province in November which left 57 people dead.

Those charged include Andal Ampatuan Snr, formerly a provincial governor and ally of President Gloria Arroyo.

Mr Ampatuan's son of the same name has already been charged with murder over the attack on a rival political family and journalists travelling with them.

The charges come as campaigning opened for the presidential elections.

Prosecutor Leo Dacera of the Department of Justice said those charged had been positively identified as "direct participants in the commission of the crime of murder", the AFP news agency reported.

The agency quoted justice department papers as saying that all the accused were "answerable as co-principals regardless of the extent or degree of their participation".

It was unclear how many of the accused were already in police custody.

The victims were part of a group on their way to file the candidacy of one of their leaders, Ismael Mangudadatu, for the May elections.

Several women were among the group, including Mr Mangudadatu's wife and pregnant sister.

They were ambushed and gunned down by around 100 armed men - their bodies were found in a mass grave in a secluded mountainous area of the province.

Mr Ampatuan Snr is the head of powerful Ampatuan clan which controlled local politics in Maguindanao and ran a private army.

He has served in the Philippines Congress and won the governorship of Maguindanao unopposed for several terms.

His son, Andal Ampatuan Jr, was reportedly planning a similarly unopposed run to replace his father, but then Mr Mangudadatu decided to run as well.

He denies the charges and is currently awaiting a bail hearing.