Strong Egypt Party leader Abdel-Moneim Abul-Fotouh, a critic of former President Morsi, called on interim president Adly Mansour to step down after 42 people were killed in clashes between the army and pro-Morsi protesters at the Republican Guard headquarters on Monday. 

Abul-Fotouh, who resigned from the Muslim Brotherhood shortly after the 2011 uprising, told Al Jazeera that the incident was "a horrible crime against humanity and all Egyptians." 

Earlier on Monday, the Salafist Nour Party, which had initially agreed on Wednesday to the ouster of President Mohamed Morsi, announced that it "will withdraw from the political process" in response to the incident.

"We wanted to avoid bloodshed, but now blood has been spilled. So now we want to announce that we will end all negotiations with the new authorities," Nour added."We wanted to avoid bloodshed, but now blood has been spilled. So now we want to announce that we will end all negotiations with the new authorities," Nour added.

President Morsi was deposed by Egypt's Armed Forces on Wednesday following nationwide protests calling for his ouster. Judge Adly Mansour, the head of the High Constitutional Court, was sworn in as the country's interim president on Thursday. 

Morsi's removal sparked anger among his supporters, mainly Islamists, spearheaded by the Muslim Brotherhood.

At least 42 were killed and over 300 injured during clashes on Monday morning between supporters of former president Mohamed Morsi and the army at the Republican Guard headquarters in Cairo's Nasr City. 

In an official statement published by Al-Ahram Arabic news website, the army said an "armed terrorist group" attempted to break into the Republican Guard headquarters in the early hours of Monday and "attacked security forces."

One officer died and 40 soldiers were injured, including seven in critical condition, the statement said.