Politicians added their voice to those of local people who have questioned the handling of the disaster by the emergency services, as the funerals of the 64 killed took place.
The president of the League of Firefighters, Jaime Marta Soares, said Wednesday he believed that arson had caused the fire, contradicting an earlier account by police.
On Sunday, police chief Almeida Rodrigues had ruled out arson, blaming dry thunderstorms for the blaze after saying they had found a tree hit by lightning.
But Marta Soares told local news media the fire had already been burning for two hours before the storm started Saturday.
"I believe, until there is evidence to the contrary, ... that the fire was of criminal origin," he added.
"The country needs clear answers to legitimate doubts," said the president of the parliament Eduardo Ferro Rodrigues, reacting to the claims.
He was addressing lawmakers during a special parliamentary session in memory of the victims of the fire, which has injured more than 200 people.
Questions also remain over how so many people could have died, most of them perishing on a single road that locals say should have been sealed off by first responders.
Early Wednesday, firefighting planes flew sorties over the smouldering forest canopy in the central Pedrogao Grande region, dropping water to bring the blaze there "under control" late afternoon, regional civil protection head Vitor vaz Pinto said.
By the evening, firefighters -- 1,500 were mobilised in all -- and firefighting planes were concentrating on fires in the area around Pampilhosa.
The blaze had appeared to be under control on Tuesday, only for it suddenly to flare again, forcing authorities to evacuate 40 hamlets near the village of Gois, not far from Pampilhosa.
Officials expressed concern that some residents were refusing to leave homes threatened by the flames.
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Questions, anger mount
In the tiny village of Alcafaz, near Gois, local people said they had stayed on to fight the fire.
"They told us the fire service would come but they never arrived," said Jose Antonio Gomes, 55, columns of smoke still rising in the hills around the village.
At another hamlet, Candosa, 33-year-old Sergio said he had worked "all day and all night without anyone coming" to help as residents themselves put all hands to the pump.
He says no one came to evacuate them, and locals had to drive the elderly to safety.
As he stood there with others, columns of smoke and flames were appearing over the top of the hill in front of the village. This time though, firefighters were on hand.
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Minute's silence
Many of those who perished were caught in their cars as they tried to flee the blaze, most of them on the N236, now dubbed the "road of death" by local media.
"My nephew died, a fireman" said Joaquim Serra da Fonseca, 68. As news of the fire spread on Saturday, his 40-year-old nephew and several colleagues rushed down the road to help.
Faced with the fury of the fire, they turned back but in the thick smoke, they apparently crashed into a car full of people, Serra da Fonseca said.
They were caught by the flames as they tried to help the passengers.
Serra da Fonseca wondered why they were allowed to take the road when police knew that a fire was raging in the area.
Martyrs
Prime Minister Antonio Costa has also asked why the N236 had not been closed to traffic. He has also called for answers as to why the emergency services communications network was interrupted.
Press reports suggested Portugal's fire plan had not been revised for four years and that the intense heat might have made some communication antennae malfunction.
As anger mounted among the relatives of those killed, the daily Publico reported that civil protection personnel and back-up fire crews only reached the fire site two hours after the first emergency calls.
Costa has called for "immediate explanations" from authorities, but insisted that there was "no evidence" of any rapid response failure.
The first funerals began late Tuesday not far from the still-burning forest.
President Marcelo Rebelo de Sousa attended the funeral of a firefighter in the village of Castanheira de Pera along with several other politicians and hundreds of locals.
A large crowd earlier had gathered in the tiny hamlet of Sarzedas de San Pedro to bury six victims.
The front page of the Correo da Manha showed images of tearful relatives next to pictures of some of those killed alongside a headline that read simply: "Martyrs".
