Supporters of deposed Islamist president Mohamed Morsi torched three churches in central Egypt on Wednesday in reprisal attacks as police dispersed demonstrations in Cairo, reports said.

The assailants threw firebombs at Mar Gergiss church in Sohag, a city with a large community of Coptic Christians who comprise up to 10 percent of Egypt's 84 million people, causing it to burn down, the official MENA news agency said.

Security officials told AFP that another two churches were attacked in El-Menia province, leaving them partially damaged by fire.

Coptic rights group the Maspero Youth Union reported the same information, accusing Morsi's Muslim Brotherhood movement of "waging a war of retaliation" against the country's Christians.

Dozens of Morsi supporters were killed on Wednesday as security forces moved in to disperse them from two major protest camps in Cairo that they have occupied since around the time the army ousted him six weeks ago.

The Coptic church backed Morsi's removal, with Patriarch Tawadros II appearing alongside army chief General Abdel Fattah al-Sisi as he announced the military coup on July 3.