The Nour Party has announced that it "will withdraw from the political process" after clashes between the army and pro -Morsi protesters at dawn on Monday left 42 dead.
"We will not be silent over the massacre that took place in front the Republican guard today," Nader Bakar, the party spokesperson wrote on his Facebook page.
"We wanted to avoid bloodshed, but now blood has spilled. So now we want to announce that we will end all negotiations with the new authorities."
The Nour Party was one of the signatories on the roadmap that head of Egyptian Armed Forces Abdel-Fattah El-Sisi announced on Wednesday in which he removed former president Mohamed Morsi from power.
Pro-Morsi protesters have been camping outside the Republican Guard headquarters in Cairo's Nasr City for several days to demand the return of Morsi to power.