Detained Abu Sayyaf militants and Jemaah Islamiyah (JI) suspects have told interrogators about the plot, although the claim is being considered "raw information" that has to be verified first, Armed forces spokesman Lt. Col. Daniel Lucero said.
"But we dont have to disregard such information. We dont like surprises and that is why we are checking on this," Lucero said.
No other details of the alleged terrorist plot were made available, but Lucero said that among those who told authorities about it was Hassan Mustafa Bakry, an Egyptian national suspected of training Muslim militants in the south.
Bakry was arrested in the southern town of Datu Piang last week.
Metro Manila police chief Director Ricardo De Leon said "precautionary security measures" have been put in place to thwart bombings in Manila, including intensified checkpoints on roads leading to air- and sea-ports.
He said police were also in close contact with Muslim leaders in Manila who gave assurances they would help in the anti-terror fight.
A spate of bombings blamed on Muslim militants killed and wounded dozens in Manila in December 2000 and there have been concerns that the governments support of the US-led war in Iraq has made the Philippine vulnerable to further attacks.
The Abu Sayyaf is a small group of Islamic militants tagged by the US and Philippine governments as a terrorist organization. It is wanted for the kidnapping deaths of two Americans in recent years and a string of bombings and attacks in the south.
Security officials here say the group once had links with Osama bin Ladens Al-Qaeda network, whose Southeast Asian front is believed to be the JI. AFP