A group of self‑proclaimed military rebels claimed responsibility for the explosion and warned of an "explosive protest" against President Gloria Arroyo this month. Another blast exploded on a street in Makati city, the financial district, wounding a boy. And a grenade with the safety pin off was disarmed by police who found it in a garbage bin near the National Printing Office.

Arroyo's chief of staff Michael Defensor blamed unidentified anti‑government elements waging "scare tactics" against the state.

In a speech before the Foreign Correspondents Association of the Philippines two days later, the President said she will serve her full term despite calls for her to resign. She said she is the only person who is fit and experienced enough to lead the nation during the transition to a parliamentary system of government.

A group describing themselves as "reformist" military officers claimed in a statement to news agencies that it "started today a series of explosive protest activities that will continue and even escalate until Gloria Arroyo leaves the presidency".

Earlier this year the government said there have been unsuccessful efforts by unknown groups to recruit military units to launch a coup against Arroyo.

She survived a brief military rising by more than 200 soldiers who took over Manila's financial district in July 2003. Last year the president also survived an impeachment complaint launched by the opposition, which accused her of stealing the May 2004 election.

The group of presumed military rebels demanded the immediate resignation of the cabinet, "or they shall become part of the explosive protest that will increase in degree in the coming days". It did not mention any specific incident.

Meanwhile, fugitive military officer Lawrence San Juan, who escaped last month while on trial for the 2003 mutiny, said his group "will take action" before the end of the month.

Interviewed by Manila‑based Radio Mindanao Network, San

Juan claimed his group was in talks with 10 active‑duty

generals, but gave no other details,

The noontime blast was clearly heard around the Malaca±ang palace compound in central Manila, briefly interrupting a lunch hosted by the president in another section of the compound.

It destroyed a trash can full of garden refuse in the palace grounds.

Police and presidential security guards sealed off the area. Military explosive‑sniffing dogs were brought in and the remains of the trash bin were taken away for forensic tests.

The dog units failed to find any explosive residue.  Presidential Security Group chief Brigadier‑General Delfin Bangit said he was not ruling out the possibility that "combustible chemicals like alcohol or some other compound" caused the explosion.

Defensor said it was business as usual for the president, "but I'm sure as a person she's worried about the situation".

Armed forces chief of staff General Generoso Senga said the authorities were monitoring unidentified people who are trying to organise an attempt to "destabilize" the government.

Arroyo called an emergency cabinet meeting following the blast, Defensor said.

"I'm sure that this is part of the scare tactics being initiated by (people) who would like to destabilize and to bring down the government," he added.

Defensor said the tactic was "disheartening" when the Philippines is focused on rescue efforts for some 1,400 people buried under a massive landslide on the central island of Leyte.