The liberal Constitution Party has expressed its support for journalists and activists attacked at a peaceful protest outside the Muslim Brotherhood headquarters in Cairo on Saturday.

The security authorities must take measures against those responsible for the attacks, said a party statement on Sunday.

The party blamed the Muslim Brotherhood, from which President Mohamed Morsi hails, for the violence.

“This attack is a clear example of the Brotherhood’s lack of respect for the most basic forms of peaceful free expression. It also fails to respect the right of journalists to do their job without having their lives endangered,” the statement asserted.

The Constitution Party—founded by reform campaigner and former presidential candidate Mohamed ElBaradei—called on judicial authorities to investigate claims filed by a number of journalists who were attacked by Brotherhood 'militias' on Saturday.

The attacks were recorded on video and audio, the statement added.

Moreover, the statement condemned the interior ministry for failing to deal with the “noticeable growth of Brotherhood militias that follow the orders of President Morsi and have the direct support of the prosecutor-general.”

On 10 March, the prosecutor-general made controversial statements about citizen's arrests which were said by some to open a dangerous precedent.

"Egypt's prosecutor-general urges all citizens to exercise their right, granted by Article 37 of the criminal procedures law of 1950, to arrest anyone committing a crime and to refer them to the authorities," a statement by the proscutor-general's office said. 

Violence between pro- and anti-Brotherhood forces broke out on Saturday, shortly after a meeting between Brotherhood Supreme Guide Mohamed Badie and Hamas leader Khaled Meshaal at the Brotherhood headquarters in Cairo's Moqattam district.

The Muslim Brotherhood denies so-called militias exist, but opponents allege they have been used to quell anti-Brotherhood protests in recent months. In December 2012, Muslim Brotherhood supporters attacked a peaceful sit-in outside the presidential palace in Cairo, killing at least 10 people.