But as clashes broke out later on Sunday, five people were killed.

A 26-year-old man died and several others were wounded as protesters attacked the Cairo headquarters of the Muslim Brotherhood, a hospital official said.

Television pictures showed the building on fire as dozens of people attacked it, throwing stones and fire bombs.

Supporters of the Brotherhood fired buckshot at the attackers in a bid to repel them. Later, automatic weapons fire could be heard around the building.

Gehad al-Haddad, a spokesman for the Islamist movement, said around 150 "unidentified thugs" had attacked the offices.

Three people were killed in the central province of Assiut when gunmen on a motorbike opened fire on protesters, a security official said.

One person died and 40 others were injured when supporters and opponents of Morsi clashed in Beni Sueif province, south of Cairo.

Both those incidents took place outside offices of the Freedom and Justice Party, the political arm of the Muslim Brotherhood.

"Dialogue is the only way through which we can reach an understanding...," Morsi's spokesman Ehab Fahmy told reporters.

"The presidency is open to a real and serious national dialogue."

But as chants of "Leave!" rang out around Cairo, the main opposition National Salvation Front called for a campaign of peaceful civil disobedience.

They urged Egyptians to stay on the streets until Morsi stepped down.

One opposition leader called on the army to intervene if Morsi refused to quit.