Large crowds were again seen streaming into Tahrir Square on Monday - defying attempts by security forces to end the protests in what had been the symbolic heart of demonstrations against Hosni Mubarak earlier in the year.

TV footage showed tear gas being fired into the protesters, while fire bombs and chunks of concrete were reportedly being lobbed back at the police.

In recent weeks, protesters - mostly Islamists and young activists - have been holding demonstrations against a draft constitution that they say would allow the military to retain too much power after a new civilian government is elected.

State television reported in the early hours of Monday that a truce had been agreed between the security forces and the imam of Tahrir Square's main Omar Makram mosque, but it did not apply to streets leading to the interior ministry where much of the fighting has been taking place.

TV footage showed tear gas being fired into the crowds as security forces again attempted to disperse protesters.

This is the longest continuous protest since President Mubarak was ousted in February and casts a shadow over elections due to start next week.

The latest violence is some of the worst in months between the Egyptian authorities and demonstrators.

Amr Moussa, former secretary-general of the Arab League and now a presidential candidate in Egypt, told the BBC World Service that the use of force against the protesters could not be justified.