A tank on a street in Cairo
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Egypt crisis: Cairo crowds gather for rallies

Crowds are gathering in the Egyptian capital Cairo for rival rallies as emotions run high ahead of a referendum due to take place on Saturday.

Largely secular opposition groups are converging on the presidential palace as Islamists gather in Tahrir Square.

Islamist President Mohammed Morsi, who called the vote to ratify a new constitution, has asked the army to maintain security.

Egypt has asked the IMF to delay a loan because of political turmoil.

The BBC's George Alagiah and Jon Leyne describe the scene at opposing protest points.

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