CAIRO, July 2 (Reuters) - Egyptian troops are preparing to deploy on the streets of Cairo and other cities if necessary to prevent clashes between rival political factions, military sources said on Tuesday.

General Abdel Fattah al-Sisi, the head of the armed forces, gave the Islamist President Mohamed Mursi 48 hours on Monday to end a crisis or face a solution imposed by the military. He said he was responding to demands from millions of protesters who want Mursi to resign.

The sources told Reuters that rapid reaction forces had been ready since last Friday to move quickly to protect demonstrators from attack.

They were wary of militant elements among both Islamists and their opponents, including remnants of the internal security apparatus of Mursi's ousted predecessor Hosni Mubarak.

U.S.-built Apache helicopter gunships circled over downtown Cairo on Tuesday afternoon, where thousands of anti-Mursi protesters were gathered on Tahrir Square. (Reporting by Yasmine Saleh; Writing by Alastair Macdonald)