MANILA, PHILIPPINES - RIVAL opposition groups buried the hatchet and joined forces on Friday to stage the largest anti-government protest in years to press for the ouster of Philippine President Gloria Arroyo.

Security forces went on full alert as more than 15,000 people marched on the financial district of Makati to call for Mrs Arroyo's removal, officials said.

Former presidents Corazon Aquino and Joseph Estrada were seen sitting side by side, apparently for the first time in public, flanked by opposition politicians, Roman Catholic bishops, priests, nuns, leftist activists and businessmen.

Placards saying 'Gloria, Resign' were brandished, along with a giant effigy of a red Mrs Arroyo devil.

'This will be the strongest rejection yet of Mrs Arroyo,' said Renato Reyes, secretary general of the leftist political group Bayan.

Police and press estimates set the crowd at 15,000 but well short of the 50,000 that organisers had hoped for.

Even so this was the largest gathering of anti-Arroyo forces since renewed allegations of corruption against her surfaced earlier this month.

The latest corruption scandal stems from accusations by an ex-government official that the president's husband and a key political ally had allegedly sought kickbacks in a failed 329-million dollar (S$458 million) broadband deal with Chinese company ZTE.

Forces on guard
About 5,000 police have been deployed around the capital to maintain peace but national police chief Avelino Razon denied accusations that his men were preventing marchers from outside the city being able to enter to join the rally.

Thousands of troops were in a state of readiness in barracks around Manila in case they were needed as back-up.

'The armed forces of the Philippines remain on red alert,' said military chief General Hermogenes Esperon.

Although billed as an interfaith rally not all religious groups attended.

The influential Catholic church bishops earlier this week issued a statement stopping short of calling on Mrs Arroyo's resignation but urged her to 'clean up corruption' in her administration.

Previous street protests against Mrs Arroyo have had disappointing results, drawing only about 5,000 people and not the tens of thousands organisers had hoped.

In another development, national police spokesman Senior Superintendent Nicanor Bartolome said the police had arrested a foreign national allegedly involved in a plot to assassinate President Arroyo.

'The foreign national was arrested in connection with previous reports about some terrorist plot involving the president,' said Mr Bartolome.

However, he would not disclose any further details, saying that 'follow-up operations are ongoing.' -- AFP