CAIRO — Thousands of angry Egyptian women joined a fifth day of protests in downtown Cairo to voice outrage over what they said was the military’s abuse and mistreatment of female demonstrators.

“Egyptian girls are a red line,” they chanted during a peaceful march from Tahrir Square through the center of the Egyptian capital, while male protesters formed a protective line around them. “Down with the military rule!”

Some carried posters and pictures of women they said were beaten, stripped and assaulted in recent days, including one woman who was captured on video as military police stripped off some of her clothing to expose her bra and then appeared to stomp on her body.

The footage has been circulated widely on social media sites, fueling a growing public anger toward the Supreme Council of the Armed Forces, which has been ruling the country since the overthrow in February of President Hosni Mubarak.

“That girl … revealed the brutality and atrocities carried out by the army,” said one female protester who did not want to be identified. “We don’t trust them anymore. They should cede power immediately.”

Sensing the public frustration, the military council quickly issued an apology Tuesday and vowed to punish those responsible for the mistreatment of women. The statement expressed “deep regret to the great women of Egypt” and reaffirmed their right to participate in the democratic transition.

The military’s expression of regret was a stark reversal of its denials in recent days that soldiers had used excessive force against demonstrators.