Scuffles have broken out in Egypt's capital Cairo ahead of the trial of former President Hosni Mubarak. Riot police are keeping apart anti- and pro-Mubarak crowds that have gathered outside the police academy courthouse where the trial is taking place. The 83-year-old is accused of ordering the killing of protesters during the uprising earlier this year that ended his rule. He denies the charges. This is the third hearing of the trial. The judge has banned live TV coverage. Four police officers, including a top officer, who worked in the operations room at the time are due to testify. Emotions are running high outside the court, situated on Cairo's outskirts, reports the BBC's Bethany Bell from the scene. Some people are chanting in favour of Mr Mubarak and others saying he should hang. Compulsive viewing A helicopter reportedly bringing an ailing Mr Mubarak from the hospital has landed in the court grounds. State television say his two sons Gamal and Alaa, as well as other defendants, have also arrived. Their trial began on 3 August and TV images showing Egypt's leader for 30 years in a cage on a sick bed in court has been compulsive viewing for people across the Arab World. But Judge Ahmed Refaat ruled at the last session that the cameras would no longer be allowed in court. He was said to have been exasperated by the army of lawyers showing off for the benefit of television in court. Observers have said the move should make the work of the court easier, although opponents of Mr Mubarak have said this may be a cover-up signalling the court has done a deal with the defendants. The government daily newspaper, Al Ahram, said four police officers responsible for operations in the central security force would take the stand on Monday. They include the head of communications, named as Gen Hussein Saeed Mohamed Mursi. The victims' families want to know what orders Mr Mubarak gave to his officials as police tried to stop the 18 days of mass protests in January and February. Mr Mubarak resigned on 11 February, but not before some 850 people had been killed in the violence. The trial of Mr Mubarak, and his sons Gamal and Alaa, has been merged with that of former Interior Minister Habib al-Adly, who is also accused of ordering the killing of protesters. All of the defendants deny the charges.