At least one person is dead after Egyptian troops opened fire on mostly Islamist protesters marching on a Republican Guard headquarters today in Cairo.

Soldiers of the Egyptian Army stand guard in front of the headquarters of the Egyptian Republican Guard in Nasr City (Ed Giles/Getty Images).

The protesters were demanding that ousted President Mohammed Morsi be returned to power. The shooting came as tens of thousands of Morsi's supporters rallied around the country, chanting, "Down with military rule."

Hundreds of the Morsi supporters were marching toward the Guard building, where Morsi had been staying at the time of his ouster. He's now in military custody at an unknown location.

The crowd approached a barbed wire barrier where troops were standing guard around the building. When one supporter hung a sign with a picture of Morsi on the barrier, the troops tore it down and told the crowd to stay back. A protester hung a second sign, and the soldiers opened fire on the crowd.

An Associated Press photographer saw several protesters fall to the ground, wounded. At least one had a head wound, and fellow protesters covered him with a blanket, declaring him dead.

The shooting threatens to escalate Egypt's confrontation. Supporters of Morsi -- largely Islamists -- are rejecting the army's ousting of the country's first freely elected president. The casualties may fuel calls by some in the Islamist movement for violent retaliation.

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