Tahrir Square filled with demonstrators overnight Thursday, voicing support for Islamist presidential candidate Mohamed Morsy.

They say his rival in the run-off, Mubarak's last prime minister Ahmed Shafik, can only win using fraudulent methods which were common practice under the old regime.

A war of words has been raging since polls closed Monday with both camps claiming victory.

Shafik told supporters he was confident that the Electoral Commission would declare him the winner.

But there is widespread concern that the interim army rulers, who recently dissolved parliament and changed constitutional arrangements, are attempting to retain power whoever is declared the winner.

This man rejects the constitutional decree and says it, like the military council, is illegitimate.

The Electoral Commission plans to announce the results of the presidential run-off on Saturday.

Lily Grimes, Reuters