Supporters of ousted Islamist president Mohamed Morsi broke into a traffic unit in Helwan in south Cairo district on Thursday and set fire to the office and vehicles inside, security sources told Al-Ahram's Arabic news website.

The attackers torched a car and a police motorcycle, and damaged windows and wooden desks. Firefighters arrived and brought the fire under control, and police arrested six of the attacks, sources added.

Sources to A-Ahram Arabic news website that the attack had been in retribution for the deaths of two pro-Muslim Brotherhood demonstrators during clashes with police in an area near Helwan on Tuesday. The fighting renewed on Thursday when assailants stormed the traffic unit, throwing Molotov cocktails and attacking the security personnel inside.

The Brotherhood has repeatedly denied carrying out attacks on security forces.

Traffic departments are controled by Egypt's police forces, which have been targeted in near-daily attacks by Islamist militants since Morsi's ouster in July.

A senior security official in Cairo, Major General Mohamed Qassem, said that investigations will be conducted to arrest the remaining suspects.