Police in Australia say they have foiled a terrorist attack after the arrests of 17 people in Sydney and Melbourne. Officers raided 23 homes in the early hours, as part of the country’s largest anti-terrorism operation.The New South Wales chief of police said a potentially catastrophic attack had been averted. Among those detained is Abu Bakr, an outspoken Algerian-Australian cleric, who has publicly praised Osama bin Laden. Outside the court in Melbourne, angry supporters of some of the suspects clashed with journalists and cameramen. Nine people have been charged with membership of a terrorist organisation. The seven arrested in Sydney are being held on charges of preparing a terrorist act by manufacturing explosives. An eighth man is in hospital after he was shot during the raids. The operation came nearly a week after Australia’s anti-terrorism laws were changed to give police greater powers.