Protesters at the epicenter of the 18-day protests that forced former president Hosni Mubarak to step down stressed "unity and public will," ignoring the scorching sun.

A preacher on the square urged the Egyptians to unite and stand with the supreme military council until it transfers power to an elected president.

Despite an agreement among various groups, fears emerge about possible tensions between the Islamist and secular groups who have been camping out on the square since July 8.

The protest on July 29 was marked by the participation of the Muslim Brotherhood members and the Salafists.

About half a million of Salafists joined the "public will and unity" protest on July 29 nationwide, official MENA news agency said, quoting a Salafi group official on the Tahrir Square. The Salafists expressed full support for the Supreme Council of the Armed Forces, which took power on February 11.

In Arish city in the northern part of the Sinai Peninsula, deadly clashes occurred when a group of armed men attacked a police station, forcing the security forces to fight back.

At least three people, including an 11-year-old child and an army officer, were killed and 12 others injured in the fighting. But a local hospital source put the death toll at four.

The Supreme Council of the Armed Forces has sent a military plane to transfer the injured to a military hospital.

In Suez, thousands of people took to the streets chanting slogans "Islamic jurisdiction should be applied."

Youth groups and some parties have accused Islamist groups of taking advantage of the rally to expand their influence, as they held banners calling for the application of Sharia and Islamic law.

By July 29 evening, Islamists left Tahrir Square. Secular groups vowed to continue their demonstration.

The rally came ahead of trial of Mubarak and his two sons due in Cairo on August 3. Ex-interior minister Habib el-Adli and six of his aides, a fugitive businessman will stand trial with Mubarak. They face charges of killing protesters and corruption.

Mubarak's trial would be held in a police academy, instead of the Cairo Expo center which was announced on July 28, state TV reported on July 29. But the change of venue has not been officially announced.