Some 31 people were injured in clashes that erupted Friday near the Muslim Brotherhood's (MB) headquarters in the Egyptian capital of Cairo between MB supporters and opponents, a medical source told Xinhua.

Mohamed Sultan, head of Egypt's Ambulance Authority, said "The injuries varied between wounds and bruises and there were no injuries from gunshots."

The injured were taken to the National Bank and Moqattam hospitals nearby, said Sultan.

A dozen security and armored vehicles, as well as about 15 ambulances, were deployed around the headquarters in Moqattam district where clashes raged on.

An eyewitness told Xinhua that some protesters threw stones toward the security forces separating the two sides, but the forces "did not respond ... and remained in their position to protect the headquarters."

"Sound of gunfire was heard but the source and type are unknown, " the witness said.

Over 20 political parties and movements, mostly liberals, including Al-Dostour Party and Free Egyptians Party, in addition to some 30 public figures, have called for staging a rally dubbed "Friday of restoring dignity" on Friday outside the MB headquarters.

Meanwhile, in Manial district of Giza, some anti-MB protesters broke into the headquarters of the group's political arm Freedom and Justice Party (FJP), according to state-run Al-Ahram Online news website.

Anti-MB protesters across the country have been demanding holding presidential election in September under full international supervision, sacking the current government and prosecutor-general, and drafting a new constitution to replace the newly-drafted "Islamist-dominated" one.