By Maggie Fick
CAIRO (Reuters) - Thousands of supporters of Egypt's ousted Islamist president Mohamed Mursi marched through districts of Cairo and other cities on Friday to demand his reinstatement, ignoring warnings that security forces would open fire if protests turned violent.
After a relative lull following the arrests of many Muslim Brotherhood leaders, the Friday rallies were the movement's biggest show of defiance since clashes two weeks ago in which hundreds of protesters were killed.
A Health Ministry official in Port Said, on the Suez Canal, said one protester had been killed and 21 injured in clashes between supporters and opponents of Mursi.
The only reported clash between protesters and security forces was outside a mosque in Giza, on the outskirts of Cairo, according to state television.
The army-backed government has arrested most of the leaders of Mursi's Muslim Brotherhood since he was toppled on July 3, suffocating protests and all but silencing the movement that ruled Egypt for a year.
Friday's demonstrators appeared to have chosen to hold numerous scattered protests and to avoid Cairo's bigger squares, where police and tanks were deployed in force, or the scenes of earlier protests such as the pro-Mursi street camps where security forces shot dead more than 600 people on August 14.
Just after Friday prayers around 500 protesters set off from central Cairo's Sahib Rumi mosque chanting, "Wake up, don't be afraid, the army must leave!", "The Interior Ministry are thugs!" and "Egypt is Islamic, not secular!"
By mid-afternoon, thousands were marching in several other Cairo districts and suburbs.
Soldiers were joined by helmeted police in black uniforms and bulletproof vests, armed with tear gas guns and semi-automatic rifles, in manning checkpoints near the protests. They blocked access to one of the bridges over the Nile.
Marches of a similar size were held in Alexandria on the coast, several cities in the Nile Delta, the three Suez Canal cities of Suez, Ismailia and Port Said, Assiut and others.
Earlier in the day an Egyptian-born, Qatar-based Muslim cleric exhorted Egyptians to return to the streets to challenge the military-backed government and restore Mursi to power.
The comments, made during Friday sermons broadcast by Qatari state television, could further worsen ties between Doha and Cairo that have already been damaged by Mursi's ouster.
"You Egyptians, go out, all of you, men, mothers, daughters even children. This is a religious duty on all Egyptians!" Sheikh Youssef al-Qaradawi said.
The crackdown on Islamists has soured relations between Egypt and Qatar, a wealthy Gulf Arab state and U.S. ally that had given Cairo $7 billion during Mursi's administration.