Riot police have sealed off the Philippine Marine headquarters, after a colonel urged citizens to defy a ban on rallies and gather at the base to protect officers implicated in what authorities say was a foiled coup.

There were songs and prayers at the gate of the Marine base, where a small group of nuns and others gathered in a show of support.

The crisis began when a Marine commander, Major General Renato Miranda, was relieved of his duties. A military spokesman, Triston Kison, told local television the commander was not forced out.

"He requested his relief for personal reasons," he said.

The spokesman said General Miranda was not implicated in the alleged coup plot. The military named Marine Colonel Ariel Querubin as a key figure in a plot to withdraw support from President Gloria Arroyo.

The colonel appeared before reporters gathered at the base, and appealed for people to come to the Marine camp to, in his words, "protect us." He confirmed that Marines had planned to walk out Friday, the day of the alleged plot, in a show of support for anti-Arroyo demonstrators.

President Arroyo said she declared an emergency because of the alleged plot, and efforts by the opposition to unseat her.