Security officials on Thursday reported uncovering plots to kill President Gloria Macapagal Arroyo and bomb foreign embassies, just as opposition leaders were calling for more protests urging the unpopular Philippines leader to resign.

Brig. Gen. Romeo Prestoza, head of the Presidential Security Group, said the Al Qaeda-linked Abu Sayyaf group and its allies were behind the planned attacks.

Few details were announced. That sparked opposition claims the government was using scare tactics in hopes of curtailing an anti-Arroyo demonstration Friday in Manila's financial district and a Sunday prayer rally involving the Roman Catholic Church and a democracy icon, former President Corazon Aquino.

Arroyo, a staunch U.S. ally plagued by long-running Islamic and communist insurgencies, has lurched from crisis to crisis since taking over in the country's second "people power" revolt in 2001, fending off three impeachment bids and four coup plots. She has two years left in her term.

Her latest challenge intensified last week when former government consultant Rodolfo Lozada Jr. linked an ex-elections chief and Arroyo's husband to an allegedly overpriced $330 million government Internet broadband contract — a contract the president canceled. Both men have denied the allegations, and Arroyo has not spoken directly about her husband's alleged involvement.

Officials already had announced that security forces were going on high alert over concerns that communist rebels planned to infiltrate Friday's protest by leftist groups and a prestigious group of business executives, the Makati Business Club.

A military spokesman, Capt. Carlo Ferrer, said intelligence reports indicated the rebels planned "to create confusion and chaos." The rebels vowed Wednesday to intensify attacks to weaken the government, but they have largely refrained from assaults that could hurt civilians.

The military chief of staff, Gen. Hermogenes Esperon, said the assassination plot reportedly involved a sniper ready to attack Arroyo when an opportunity arose.

Arroyo's planned visit to the Philippines' premier military academy this weekend in the northern city of Baguio was canceled and her remaining schedule was "under assessment," said Prestoza, the Presidential Security Group head.

Prestoza said police uncovered the assassination plot last week. "It's not only the president who is the target, but also other people ... and embassies," he said, without offering any details.

U.S. Embassy spokeswoman Rebecca Thompson said she had heard media reports about the alleged plot but would not comment further.

Renato Reyes, one of the organizers of Friday's protest, scoffed at the government's announcement.

"Obviously this is a very desperate tactic to create an atmosphere of terror and scare people to prevent them from joining the protest actions tomorrow," he said.

The military commander denied that.

"We are simply acting as security forces and so we have deemed it necessary that we come out in the open about our assessment of the situation," Esperon said.

A police counterterrorism officer said a captured Abu Sayyaf member told investigators late last year that his comrades, working with Indonesia-based Jemaah Islamiyah and Manila-based Filipino Islamic converts, planned a bomb attack apparently in December aimed at unspecified targets in Baguio, a mountain resort city.

Philippine security officials speculated the targets could include Arroyo, who usually spends Christmas Eve with her family in Baguio but did not do so in the latest holiday, or U.S. diplomats, who have a consulate in Baguio, the officer said.

The officer, who agreed to discuss the matter only if not quoted by name because he was not authorized to talk to journalists, said investigators found no evidence to back up the Abu Sayyaf member's claim. No bomb attack occurred in Baguio in December.

Abu Sayyaf and its allies have been blamed for numerous kidnappings, beheadings and bombings, including an explosion that triggered a fire which killed 116 people on a ferry in Manila Bay four years ago.