Tens of thousands of protesters have massed across Egypt to voice growing frustration with what they see as a slow pace of government reforms and delays in prosecuting former officials linked to killings of pro-democracy demonstrators.

Protesters packed Cairo's Tahrir Square on Friday for one of the largest rallies since the 18-day revolt that led to former President Hosni Mubarak's resignation in February.

Activists have pitched tents in the square, where Egyptians are chanting and waving flags.

Witnesses say shots were fired during a smaller protest in Suez on Friday. Rallies are also underway in cities including Alexandria and Sharm el-Sheikh, where Mr. Mubarak remains detained in a hospital. His lawyers say he is battling cancer.

The rallies follow several legal decisions that have angered some Egyptians. They say trials of former officials are not transparent enough and are not moving fast enough.

Earlier this week, hundreds of protesters in Suez attacked a courthouse and police station. They were angered by a judge's decision to uphold the release on bail of seven police officers charged with killing demonstrators during the pro-democracy uprising.

On Tuesday, a Cairo court acquitted three of Mr. Mubarak's former Cabinet ministers of corruption charges.

Wednesday, in an apparent bid to stem mounting protests, Egypt's security chief announced plans to dismiss hundreds of police officers linked to the deadly crackdown.

Last week, more than 1,000 people were injured in clashes between police and protesters in Cairo. The demonstrators were urging the country's military leaders to speed up the prosecution of officials blamed for killing protesters in the lead-up to Mr. Mubarak's departure from office.

At least 850 people were killed during the 18-day revolt that culminated with Mr. Mubarak's resignation.