Officials said that marines were guarding highways around the capital, while riot police were on standby at vital installations.
  
Left-wing groups and those allied with the political opposition threatened mass protests on Independence Day to call for Arroyo's resignation.
  
Opposition senators have called on Arroyo to resign amid allegations she rigged last year's presidential polls to beat Fernando Poe, the country's most popular movie star and a friend of deposed president Joseph Estrada. 

Challenge
  
The president has resisted the calls for her resignation and called for unity. 
  

President Gloria Arroyo has been
accused of corruption

"I am calling on everyone to do away with dirty politics and focus our energies to improve the economy," Arroyo said in a speech to mark the country's independence from Spanish rule 107 years ago.
  
"My countrymen, the flag is the symbol of power and determination. Mark it in stone, I will show this power and determination to uphold democracy and guide the country in the right direction."
  
She accused her critics of creating the image that the country was "nothing more than a private sandbox for political intrigue".

This view, she said, was dangerous and irresponsible as she challenged the opposition to present a viable alternative to her leadership.