By Rachel Harvey
BBC South East Asia correspondent
A state of emergency was declared in Maguindanao province
Officials in the Philippines say 19 people being investigated over last week's massacre of 57 people have been placed on a security watch list.
The move is to prevent the suspects from leaving the country but falls short of an arrest warrant.
Twelve of the 19 people are relatives of the only suspect who has so far been charged, Andal Ampatuan Jr.
Among them is his father, the head of a clan which has long controlled the region where the massacre took place.
Andal Ampatuan Jr is now in custody, charged with multiple counts of murder.
The Philippines Justice Secretary, Agnes Devanadera, has told the BBC that 12 of his relatives, including his father, are on an official watch list.
Asked whether some on the list may have already fled the country, Ms Devanadera replied "that's not impossible".
Meanwhile, armed troops now surround the Ampatuan family home in Maguindanao province and hundreds of reinforcements are on their way.
On Thursday the entire police force - more than 1,000 officers - of Maguindanao was removed from duty.
Decisive moves, but many Filipinos say they will not be satisfied until all those responsible for the killings are brought to justice.