Police fired tears gas against the stone-throwing protesters in Tahrir Square, where thousands have been camping out for several days in a bid to convince Morsi to rescind the decree.

State television confirmed that police had used tear gas to disperse protesters who were gathering near the US embassy.

Last week, Morsi signed a constitutional declaration exempting all his decisions and laws of judicial review and barred courts from dissolving an Islamist-controlled assembly drafting a new constitution.

The decree incensed the opposition and triggered violent clashes between Morsi's opponents and backers in several parts of the country.

Scores of people were late Tuesday injured in street violence over the decree in the Nile Delta town of Al Mahla Al Koubra, reported Egyptian television.

The opposition claims that the decree gives Morsi "dictatorial" powers.

Morsi, for his part, says the measures are "temporary" and are aimed at protecting the "revolution" that toppled Hosny Mubarak.

The standoff is the worst since Morsi became Egypt's first elected civilian and Islamist president, in June.