MANILA, Philippines--Foes of embattled President Gloria Macapagal-Arroyo held a "mass for the truth" on Sunday and vowed more street protests in the coming weeks to press for her resignation.

Hundreds of students and church workers joined former president Corazon Aquino and other members of the opposition in the mass at the University of Santo Tomas in Manila.

They sang nationalistic hymns and raised clenched fists as they repeated demands for Arroyo to resign.

Also in the gathering was Rodolfo Lozada, a former mid-level government official who implicated Arroyo's husband and a political ally in a corruption case surrounding a botched telecoms deal.

Lozada's explosive testimony has led to mounting calls for Arroyo to step down, and on Friday more than 15,000 people gathered in the capital's Makati financial district in the largest protest since the scandal broke last year.

"There will be more rallies to come," said Adel Tamano, a spokesman for the political opposition. We believe that the rally last Friday has led to a snowballing effect."

He noted that universities around Manila had become major starting points for protests, with students coming out in their thousands last week.

"We are beginning to reach a critical mass," Tamano said on local radio, adding that the protests in Manila were matched by smaller rallies in key cities around the Philippines.

Aquino and another ex-president, Joseph Estrada, were the key figures in last week's protest and both called for Arroyo to step down.

Renato Reyes, secretary general of the activist group Bayan, said Friday's rally was the "strongest rejection" yet of Arroyo.

"This is an encouraging sign of political maturity among Filipinos," he said, adding that the next protest would be on March 8, to coincide with International Women's Day.

Arroyo has kept a low profile amid the anti-government protests, and her spokesman Ignacio Bunye on Sunday said she had spent Friday chairing a mining conference and visiting development projects in the countryside.

The president earlier said she would not step down until her six-year term ends in 2010 and denied that her family had profited from government deals.

She has earlier survived three impeachment bids in Congress, and put down two coup attempts.