An Islamist alliance urged its supporters to stay away from Cairo's Tahrir Square during protests Friday to avoid more bloodshed after a week in which nearly 80 Egyptians were killed.
The interior ministry warned the Islamists that it will "confront any attempts to break the legitimacy" of the interim government.
The Anti-Coup Alliance, which rejects Egypt's military-installed government, said the "coup regime is shedding blood without any respect to law or values adopted by our great people".
"So the alliance is calling for marchers to avoid places of bloodshed, be it Tahrir or other squares," said a statement from the group which demands the reinstatement of ousted Islamist president Mohamed Morsi.
It said its appeal follows calls by several intellectuals and political forces as marches to the iconic square "will lead to more bloodshed".
The alliance had repeatedly called on its supporters to march on Friday towards Tahrir, the main symbol of the Arab Spring-inspired uprising that toppled former strongman Hosni Mubarak in 2011.
"We are just limiting our marches" on Friday, the alliance said, adding it reserves "the right to protest in all squares including Tahrir, Rabaa and Nahda in the coming weeks".
Cairo's Rabaa al-Adawiya and Nahda squares were sites of a brutal crackdown by security forces on Morsi's supporters on August 14. Hundreds of people were killed in some of the worst carnage in Egypt's modern history.
"The decision was taken to calm things down after what happened on October 6," said Tareq Hussein of the Youth Against Coup group, a member of the alliance.
On Sunday fierce clashes erupted when security forces prevented Islamists from trying to reach Tahrir Square where supporters of the military were celebrating the 40th anniversary of the Arab-Israeli war.
At least 48 people were killed in those clashes, and nine others died in similar fighting in other parts of the country.
"We are just holding our breath after Sunday's massacre. The challenge to the coup is still on and this is a battle to break the will of the coup," Hussein told AFP.
The interior ministry warned Islamists that it had deployed security reinforcements in Tahrir Square and streets around it and near the US embassy in central Cairo.
"We will prevent any attempts by the Muslim Brotherhood to hold sit-ins in Nahda Square," the ministry said in a statement reported by state news agency MENA.
AFP reporters saw security forces sealing off Nahda Square and Mustafa Mahmoud Square in the capital.
At least 77 people have been killed across Egypt since last Friday, making this period the deadliest after the crackdown on Morsi's supporters in August.
Since August 14, more than 1,000 people have been killed nationwide, while more than 2,000, mostly Islamists, have been detained.
Morsi, Egypt's first democratically elected president, has been held at an unknown location since the army toppled him on July 3.