Thousands of protesters flocked to Cairo's iconic Tahrir Square on Friday for a mass rally demanding reforms as the ruling military warned it would respond harshly to any violence by activists.
Organisers called the rally to press Egypt's military rulers to keep their promises of reform after a revolt ousted president Hosni Mubarak in February.
Protesters, gathered under a scorching sun, filled a section of the square to listen to the weekly Muslim prayer sermon.
"It would be shame on the Egyptian people if they forget their revolution," the preacher said.
He attacked some of the prosecution witnesses in the ongoing murder trial of Mubarak and his security chiefs for testifying in court this week that they had not been ordered to use deadly force against protesters during the revolt.
"They must be charged with false testimony. How can a prosecution witness turn into a defence witness?" the cleric asked.
The preacher also denounced military trials for civilians. The military, which took charge after Mubarak's departure, has sentenced thousands of people to prison terms since February.
Signup to our newsletter and follow us on Facebook and Twitter!
Protesters chanted slogans against the military ruler and current de facto head of the state Field Marshal Hussein Tantawi after the sermon ended.
Ibrahim Ali, an agricultural engineer, said he had come to the capital from northern Egypt to attend the rally.
"None of the revolution's demands have been met," he said. "There is still injustice in the country."
The military, in a statement posted on its Facebook page, said it respected the activists' right to protest peacefully, but warned it would respond to violence by the protesters with "the utmost severity and decisiveness."
The interior ministry said it had withdrawn riot police stationed in Tahrir Square to allow the activists to protest unhindered, the official MENA news agency reported.
The protest was called by mostly secular and leftist activists, and is being boycotted by the influential Muslim Brotherhood movement and other Islamist groups.
Mohsen Rady, a senior Brotherhood member, told state television his movement, which is showing growing strains with the military, believed Egyptians were weary of protests.
"People have grown bored of these demonstrations," he said.
Secular activists are concerned that the military's current timetable for parliamentary elections in autumn will play into the hands of the Brotherhood by denying new political movements the time to organise into parties.
The activists are also demanding an end to the military trials of civilians.