Cairo, Egypt

“Freedom!” the crowds chanted along the banks of the Nile River in Cairo after dark Friday, defying a curfew being enforced by troops with armored personnel carriers and tear gas.

The demonstrators had been out on the street all day, not just in the capital, but in Alexandria and Suez as well, prompting President Hosni Mubarak to send troops out onto the streets for the first time in a generation.

The demonstrators surrounded a military vehicle, even climbing on top of it — and the military did not respond.

But when the protesters circled the Ministry of Information, they were greeted by police, who responded with sharp cracks of gunfire.

It’s not clear whether police shot at protesters or into the air, whether their bullets were rubber or steel, whether anyone was wounded or killed.

As the night wore on, however, police appeared to retreat to their stations, leaving the streets to the military.

In both Cairo and Alexandria, protesters greeted the troops with embraces and cheers. Demonstrators shook hands with soldiers, members of an army that is widely respected in Egypt.

The army isn’t the only side exercising restraint.

The Muslim Brotherhood sent its followers onto the streets after Friday prayers, the first time Egypt’s large and venerable — but illegal — Islamic opposition called for protest during this round of demonstrations.

And when younger Muslim Brotherhood protesters seemed ready to hurl rocks at the police in Alexandria, Egypt’s second-largest city, older men put their arms around the shoulders of the hotheads, calming them down.

Four days into unprecedented protests that have shaken Egypt, both sides seem to be holding back from the brink. How long that restraint last may determine the course of Egypt’s future.