Eight people were confirmed dead on Friday and the body of a man was found early on Saturday in the debris, a police official said. One person remains missing.
Police told Gloria Macapagal Arroyo, the president, that traces of RDX, a component of plastic explosives, had been found at the site.
"It was military-grade explosives," the expert said during a news conference.
Arroyo has ordered police to "leave no stone unturned" in their investigation and called a cabinet security meeting on Saturday with police and military officials.
Geary Barias, Manila police chief, said closed-circuit TV footage of the shopping centre was being reviewed in an attempt to identify possible suspects.
|"What is more ominous here is they may be planning a bigger attack" |
Norberto Gonzales, presidential security adviser
When a journalist asked the president who would benefit from such an attack, Arroyo replied: "It's the terrorists. Let us ask the terrorists."
Norberto Gonzales, the president's security adviser, said they had received an intelligence report that Abu Sayyaf was trying to raise funds abroad using the internet site YouTube and the blast could be used as part of this campaign.
"What is more ominous here is they may be planning a bigger attack," Gonzales said on a radio programme on Saturday.
"They will first show a sample. That means that while the bomb yesterday already was powerful, it is still just a sample."
Several days ago, Avelino Razon, the national police chief, ordered "maximum security coverage" at possible targets, including shopping centres, in the southern Philippines, after police intelligence reports of possible bombings
Abu Sayyaf is said to be linked to the regional Jemaah Islamiah group, which has been blamed for similar explosions in the past, including the 2002 Bali bombings that killed 202 people on the Indonesian resort isle.
A general alert has been issued for the rest of Manila and for the international airport.
Manila has largely been spared a spate of bomb attacks by Abu Sayyaf and other Muslim groups that have plagued the southern Mindanao region.
However, in February 2004, more than 100 people were killed when a bomb planted by Abu Sayyaf sank a ferry in Manila Bay.