CAIRO  President Hosni Mubarak struck back at his opponents on Wednesday, unleashing waves of his supporters armed with clubs, rocks, knives and firebombs in a concerted assault on thousands of antigovernment protesters in Tahrir Square calling for an end to his authoritarian rule.

Early Thursday morning, shots were fired at the anti-Mubarak protesters, a number of witnesses said. It was unclear whether the shots came from the pro-government demonstrators or from the military forces stationed in the square.

Two people were killed by the gunfire and 45 people were wounded, said a doctor at a nearby emergency clinic set up by the antigovernment demonstrators. After the gunshots, soldiers fired their weapons into the air, temporarily scattering most of the people in the square.

On Wednesday, the protesters, after first trying to respond peacefully to the Mubarak supporters, fought back with rocks and firebombs of their own. Scores of the wounded were carried back on cardboard stretchers to a makeshift clinic set up in a nearby mosque, where they were treated by dozens of doctors.