We call for justice, Benny Antiporda, head of the National Press Club, said in a statement. The whole world has shown its disgust over what happened. The media workers killed in the massacre were not armed.
The National Union of Journalists has said 59 journalists have been killed in the Philippines since 2001, without counting last week's victims. Although the press in the Philippines is among the most free in the region, reporters are routinely threatened, some are shot and some kidnapped.
Last Monday, gunmen attacked a convoy carrying the family of a man planning to run for elections next year, lawyers and the journalists. The bodies of 57 people were later found off the highway, some on a grassy hillside and some hastily buried in a pit.
State prosecutors are due to file multiple murder complaints against Andal Ampatuan Jr, a town mayor in Maguindanao province and the main suspect in the massacre, blamed on a clan feud.
On Friday, the justice department moved to stop eight other members of the Ampatuan family from leaving the country as they were also placed under investigation. The government was also planning to suspend and remove them from positions of power in the province to pave way for a fair inquiry.
In the south, soldiers and police officers were searching houses for weapons used in the murder on November 23, arresting armed followers of the Ampatuan clan. About 400 government-issued rifles were seized from a civilian militia force last week.
Wearing black shirts and bearing placards to demand an end to political killings, the protesters in Manila heckled Press Secretary Cerge Remonde who crossed a police line to talk to the journalists.
The government will do everything to give justice for all, Remonde, who was in a black shirt and armband, told the protesters.
(Reporting by Manny Mogato; Editing by Raju Gopalakrishnan and Sanjeev Miglani)