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CAIRO -- Egypt's most prominent reform advocate called on Sunday for President Hosni Mubarak to resign after the powerful military stepped up its presence across the anarchic capital, closing roads with tanks and sending F-16 fighter jets streaking over downtown.

The army's show of force appeared aimed at quelling looting, armed robbery and arson that broke out alongside pro-democracy protests and have turned the cultural heart of the Arab world into a tableau of once-unimaginable scenes of chaos.

The military made no attempt to disperse some 5,000 protesters gathered at Tahrir Square, a plaza in the heart of downtown that protesters have occupied since Friday afternoon. They have violated the curfew to call for the ouster of President Hosni Mubarak's regime, which they blame for poverty, unemployment, widespread corruption and police brutality.

Nobel Peace laureate Mohamed ElBaradei appeared in the square around 7 p.m.

"You are the owners of this revolution. You are the future," he told the cheering crowd. "Our essential demand is the departure of the regime and the beginning of a new Egypt in which each Egyptian lives in virtue, freedom and dignity."

One of the senior leaders of the outlawed Muslim Brotherhood, which wants to establish an Islamist state in the Arab world's most populous nation, told The Associated Press he was heading to Tahrir, or Liberation, Square to meet with other opposition leaders.

"You can call this a revolution, you can call this an uprising," Essam el-Erian said.

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