The police chief of the Philippines announced that the investigators of the country probing a blast that killed 11 people at an upscale Manila shopping have not found bomb fragments in the debris and haven't ruled out that it was an accident.
President Gloria Macapagal Arroyo called a top security meeting with congressional leaders and other officials to discuss explosion at The Glorietta 2 mall and security measures in the wake of the blast.
"So far we have not found bomb fragments but that is not conclusive that it was not caused by a bomb because we have not gone through the entire rubble and debris," national police chief Avelino Razon told The Associated Press.
Three government investigators told AP on Sunday it was premature to conclude that a bomb caused the blast.
The investigators, who spoke on condition of anonymity because they were not authorized to talk to the media, said they had searched a cargo storage basement where the blast most likely originated.
They said there was a possibility that fumes could have leaked from a huge diesel fuel container, or that methane gas could have escaped from a septic tank, and ignited in the tightly enclosed concrete basement.
"There is a possibility it was an accident because the facility could have used methane, especially for waste water treatment," metropolitan Manila Police Chief Geary Barias said Monday. "Anything is still possible at this time."
Barias told reporters investigators finally gained access to the basement of the mall late Sunday after removing 19 tanker loads of water, oil and diesel, which came from burst pipes.
Probers were still sifting through debris looking for possible bomb fragments, Razon said.
Chief Superintendent Luizo Ticman, head of the police task force investigating the blast, said possible sources of ignition found in the basement included a diesel storage tank, batteries and automatic switches.
Razon said it would have taken 50 kilograms of explosives to create the damage inflicted by the blast.
U.S. and Australian police and foreign and local metallurgical forensic and petrochemical experts were helping in the investigation, officials said.
"This is a very tedious process," Razon said. "It is just like looking for a needle in a haystack."
Rumors have spread by word of mouth and cell phone text messages blaming the blast on a variety of people _ including military renegades, Muslim militants and government forces loyal to Arroyo, whose administration has been linked to a string of corruption scandals.
Bunye said Arroyo will preside Tuesday over a meeting of the National Security Council, the country's policy-making and advisory body, after she appealed for national unity while the investigation into the blast continues.
Police and the military have remained on high alert and increased their visibility in public places.