The head of the Philippine Human Rights Commission says martial law should not have been imposed in the province that witnessed a recent political massacre.
The commissioner, Leila de Lima, said the massing of armed men in Maguindanao did not constitute sufficient grounds to proclaim martial law.
But she described as a positive step the filing of charges of rebellion against members of the Ampatuan clan.
The clan is accused of being behind the massacre of 57 people.
Members of a rival clan and 30 journalists were among those killed on 23 November.
The victims were part of a group on their way to file the candidacy of one of their leaders for elections in 2010.
Twenty-four people have been charged with rebellion after the massacre on the island of Mindanao last month, including several figures from the clan.
"In the initial stages of the investigation the government was overly cautious," Ms de Lima said. "But in recent days it has been really very decisive and taken bold steps."
However, she told the BBC, the imposition of martial law - declared on Saturday for the province of Maguindanao - was not warranted.
Although the government said it imposed martial law because of evidence a rebellion was being fomented, Ms de Lima said she saw no factual basis for that claim.
"Our question is - since when do you need martial law just to enforce the full force of the law?" she said.
Philippine observers have noted that President Gloria Arroyo has been politically beholden to the Ampatuan clan, and have speculated that she may find it difficult to clamp down on them.
At the same time, Mrs Arroyo is under immense domestic and international pressure to punish those behind the massacre and to clamp down on armed gangs.
"They have no choice but to really hold them accountable. It would be a bigger political suicide on the part of the incumbents now to go against the tide of public opinion," Ms de Lima said of the government.
Her comments, made in an interview with the BBC, came as the Philippine Congress is engaged in several days of debate about whether to formalise Mrs Arroyo's declaration of martial law.
Two weeks ago a clan leader and local mayor Andal Ampatuan Jr surrendered to the authorities and was charged with multiple counts of murder.
Police say Mr Ampatuan Jr organised the attack and killed many of the victims himself.
His father, Andal Ampatuan Sr - who was detained at the weekend - was among those charged on Wednesday. The patriarch is a close ally of President Arroyo.