The force of the explosion, believed to have come from a remotely detonated mortar round, also punched fist-size holes in a concrete wall of a nearby upscale compound in Makati city, officials said.

In a nationally televised statement, President Benigno Aquino said all government agencies, including the intelligence services, would not stop "until everyone involved in this heinous crime is accounted for."

"We will not allow this situation where there is fear among the people to continue," said Aquino, who visited the wounded in hospitals late Tuesday and inspected the damaged bus in a police compound.

At least one of the 14 wounded people was in critical condition and a few others have to undergo surgery to remove shrapnel from their feet, Welfare Secretary Dinky Soliman told reporters.

Aquino and other officials have not named any specific suspects but suggested they included al-Qaida-linked Abu Sayyaf militants, who have been blamed in past attacks on passenger buses, including a 2005 bombing that killed four passengers very near Tuesday's blast.

Aquino said he directed his national security adviser to reassess threats that reportedly came from terrorist groups last year and that prompted several countries, including Australia, Britain and the US, to put in place travel warnings. At the time, the government had not found the threats credible and the warnings infuriated Aquino.