The military, which has until now said it would not use force on peaceful demonstrators, has urged anti-government protesters to return home. And supporters of embattled President Hosni Mubarak, who had been largely silent since the unrest began, came out in full force Wednesday, in one case wielding whips and thundering through the crowd on horses and camels.

As dawn broke Thursday, heavy gunfire reverberated in central Cairo as the two sides continued to face off at Tahrir Square — the confrontations portending what awaits when Egypt awakes.

Egypt’s minister of health said the number of injuries in Cairo’s Tahrir Square has reached 829 — including 200 within one hour on Thursday morning, state-run Nile TV reported. The minister also said four people were killed in Tahrir Square on Thursday morning.

A national security official in U.S. President Barack Obama’s administration told CNN that the situation in the country could “turn really ugly” and the next 24 to 48 hours will be critical.

“Will the military continue to act responsibly? Or will it fracture?” said the official, who has been involved in Egypt deliberations. “Will Mubarak get it that the writing is on the wall and that he has to transition out quicker? Not sure anyone has the answers.”

Meanwhile, chunks of concretes and Molotov cocktails flew in Tahrir Square during the escalating crisis Thursday.

The wounded were being carried into the square, largely held by anti-regime demonstrators, through an entrance that leads to the nearby Egyptian Museum. Several ambulances entered and left the square shortly before 4 a.m. Thursday.

The source of the gunfire was not immediately known.

Another U.S. official said the administration’s conversations with Egyptian officials have turned tense and urgent — with the U.S. side voicing hope the military will see the reality and pressure Mubarak to step down.

While the official was encouraged by signs that the military was not involved in the violence that broke out Wednesday, allowing such fights between supporters and opponents of Mubarak to go on “could fairly be interpreted as a choice, and a troubling choice.”

This official voiced hope that “as time passes, the military will see which side it wants to be on for the good of the country and the society.”

Some chanted a prayer Thursday after a day of violent street battles in central Cairo. People also shouted, “No one hurt anyone.”