Over the weekend, I noted coup rumors flying in Manila. This morning, there are reports of a bomb blast at the presidential palace of Philippine president Gloria Macapagal-Arroyo (whose office is downplaying the incident). Bloomberg has the latest:

Two groups claiming to comprise Philippine military officers said they were behind an explosion in the presidential compound that caused no injuries or damage to buildings. Officials said the blast may have been accidental.

The blast occurred just after noon local time in a trash bin in the compound of Malacanang Palace in the capital, Manila, Presidential Security Group Commander Delfin Bangit said in a phone interview. The peso had its biggest drop in four weeks.

The explosion was “an expression of our determination and will to end the illegitimate and corrupt administration,” of President Gloria Arroyo, according to a fax received at the palace press office. The senders said they were made of two groups, the Young Officers Union and the Reformist Armed Forces of the Philippines,

The blast raised concerns about moves to oust Arroyo. The opposition last year demanded her resignation and tried to impeach her on allegations she cheated in the 2004 election. In December and January, three soldiers on trial for a 2003 mutiny escaped, vowing to resume their efforts to oust Arroyo.

AP says Arroyo was inside the palace at the time having lunch with Intellectual Property Office officials. The Philippine Inquirer identifies the two groups claiming responsibility for the blast as the Young Officers Union of the New Generation and Reformist Armed Forces of the Philippines. Presidential Chief of Staff Michael Defensor disputes the claim:

“This is not an orchestrated effort or a move being undertaken by this group,” he said, referring to the YOUNG and RAFP.

If the group was indeed behind the incident, Defensor said it was the “height of unpatriotism,” carrying this out at the time when the people’s efforts were focused on helping the victims of the landslide in Southern Leyte province.

Defensor said the administration was not scared by the threats of the group and would not be affected by them.

The blast occurred amid tight security over coup rumors ahead of the 20th anniversary this week of the “people power” revolt that ousted dictator Ferdinand Marcos.