Arroyo, who came to power in a military-led popular uprising in January 2001, said on national television that her government was in "full control" of the situation but appealed to the people to be vigilant.

She received immediate backing from Defence Secretary Angelo Reyes and military chief of staff General Narciso Abaya.

They have issued orders to arrest about 20 junior officers, many of them said to have led elite units and to be experts on explosives.

The officers, graduates of the elite Philippine Military Academy (PMA) and aged up to 32, were backed by "between 40-50" fully armed men.

Abaya said the men, the highest ranking of whom are captains, "can do a lot of damage."

Aides said the 54-year-old Arroyo was unshaken and remained at the heavily-guarded Malacanang palace, the gates of which have been barricaded by armored military and police vehicles and heavily-armed soldiers.

Scores of presidential security guards, clad in combat uniforms and armed with assault rifles, searched all vehicles passing through streets around the palace and turned away uninvited visitors, an AFP correspondent said.

Military and police personnel also secured key installations, including the Congress building. Many Filipinos were not aware of the coup attempt and Manila's nightlife remained vibrant Saturday.

Influential Philippine church leader Cardinal Jaime Sin appealed to his flock to protect Arroyo, calling for a prayer vigil at a historic shrine.

Sin is the de facto church leader in the Philippines -- Asia's bastion of Catholicism -- where more than 80 percent of the country's 80 million people are practicing Roman Catholics.

The United States embassy in Manila also expressed concern over the coup plot.

"We support the legitimate civilian government of the Republic of the Philippines," press officer Ron Post told AFP.

Arroyo warned the coup plotters of severe punishment, describing them as "fugitives from military justice."

She also warned "unscrupulous politicians who exploit the messianic complex of these officers for their naked ambitions."

Arroyo did not identify these politicians.

Rumours that a military clique was plotting to overthrow the government had gripped Manila but Arroyo dismissed them last week when she met with a group of disaffected junior officers at a dinner at the palace.

Junior military officers have complained of low pay, corruption and inadequate housing facilities for soldiers.

However military spokesman Lieutenant General Rodolfo Garcia said these complaints "are not actually the reason (for the mutiny). We believe this has a political component to it."

Allies of Arroyo's predecessor and rival Joseph Estrada could be linked to the coup plot, he said.

Amid the coup rumours last week, Estrada had warned of a possible revolt against Arroyo because she had allegedly snatched the presidency from him illegally.

Estrada, who is in jail on charges of corruption, denied any involvement in the coup but insisted he was still the legal president in a television interview.

The Philippines suffered seven bloody coup attempts by rightist military officers with ties to opposition politicians in the late 1980s, setting back economic development by years.

The latest coup attempt "is not a threat to the government, (but) this is a threat to stability," said Senator Rodolfo Biazon, a retired Marine general and armed forces chief of staff who fought the bloodiest of the coup attempts.

Defence Secretary Reyes said only a small band of officers and men were behind the latest attempted power grab and "we have this under control."

Congressional leaders condemned the revolt and said in a statement that the plotters would not find support among "our democratic people."

Arroyo is scheduled to deliver her state of the union address at the legislature on Monday where she is expected to unveil a package of political, economic, social and electoral reforms on Monday.

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