CAIRO, March 28 (Reuters) - At least five people were killed in clashes in Cairo on Friday involving security forces, Muslim Brotherhood supporters and residents days after hundreds of Islamists opposed to the military-backed government were sentenced to death.

Newspaper Al Dustour said one of its journalists, Mayada Ashraf, had died covering the fighting, the latest unrest in Egypt since the overthrow of President Mohamed Mursi, a Brotherhood leader, last July.

An Interior Ministry said in a statement that five people were killed in clashes in Cairo, blaming the Brotherhood gunmen for the deaths. A health ministry official, who declined to be named, said at least one had died from live ammunition.

It was not clear if that total included Ashraf.

Brotherhood supporters also fired birdshot and threw missiles, the ministry said. It added that 79 protesters, accused of possessing of petrol bombs and fire arms, were arrested as hundreds of Brotherhood supporters took to the streets across Egypt.

Police fired tear gas at the protesters.

The Brotherhood's press office in London blamed security forces for shooting at what they said were peaceful protesters.

Since Mursi's overthrow, the authorities have mounted a campaign of repression against the Brotherhood, killing hundreds and arresting thousands, including Mursi and most its leaders.

Friday's violence followed the announcement on Wednesday by Field Marshal Abdel Fattah al-Sisi, the man who deposed Mursi amid mass protests against his rule, that he was resigning as army chief and intended to run in a presidential election.

Supporters of the Brotherhood, outlawed and branded a terrorist group by the army-backed authorities, see Sisi as the leader of a coup against a democratically elected president.

A court sentenced more than 500 Brotherhood supporters to death on Monday, triggering clashes between security forces and protesters in which at least one man was killed.

Egypt has seen three years of political turmoil since an uprising ended President Hosni Mubarak's three decades of one-man rule. (Reporting by Shadia Nasralla; Editing by Angus MacSwan)