Feb. 20 (Bloomberg) -- 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.

Bangit and Presidential Chief of Staff Mike Defensor said the explosion may not have been caused intentionally. Defensor said it may have been fueled by lacquer thinner. He said he didn't know if it was accidentally or intentionally lit.

Peso Falls

The peso fell 0.35 percent to 51.98 to the U.S. dollar when local trading ended at 4 p.m. in Manila. That was its biggest one-day drop since Jan. 20 and its lowest level since Feb. 2.

The benchmark 91-day Treasury bill yield rose to 5.25 percent at the government's weekly auction, its highest level since Nov. 14.

The explosion ``will create a near-term reaction,'' according to Jonathan Ravelas, a strategist at Manila-based Banco de Oro. For the past several weeks we've been seeing stories on the security front and this is a lapse in security. It's going to renew concerns.''

The explosion comes after the Philippine police on Feb. 14 raised security amid speculation of a coup plot. The police deployed anti-riot units around a courthouse that held a trial for other soldiers accused in the 2003 mutiny. The military received reports that allies of the soldiers may try to free them, the Philippine Daily Inquirer reported then, citing military spokesman Tristan Kison as saying.

Elsewhere in the capital, a small explosive device detonated in Makati, injuring a 4-year-old girl, and a hand grenade was found outside a government printing office in Quezon City, ABS- CBN radio and other local media reported.

The ``pillbox'' bomb may have been made and planted by local teenagers, Makati police chief Marietto Valerio said in a phone interview. The grenade may have been accidentally dropped by a soldier, Armed Forces of the Philippines spokesman Tristan Kison said in an ABS-CBN interview.

To contact the reporter for this story: Francisco Alcuaz Jr. in Manila at falcuaz@bloomberg.net

Last Updated: February 20, 2006 05:46 EST