Unknown assailants torched "Rebel" Campaign headquarters in downtown Cairo on Friday morning using petrol bombs.

Campaign spokesman Hassan Shahin was injured in the fire, the campaign wrote on its Facebook page.

"Rebel" urged all activists to defend its headquarters and protect the millions of signed forms it has gathered from damage.

Several campaign members filed a formal complaint against President Mohamed Mursi, Muslim Brotherhood leaders Mohamed Badei and Khairat al-Shater, the Freedom and Justice Party head Saad al-Katatni, Islamic Jama'a member Assem Abdel Maged, and Muslim Brotherhood member Ahmed al-Mogheer.

"Rebel" accused all of the above of incitment to burn its headquarters and attack its activists.

"Rebel" campaign aims at gathering support from Egyptians to call for a no-confidence vote against Mursi and promote holding early presidential elections.