<sod >Police close a street where a cafe is being used to hold hostages in the central business district of Sydney Â  Australia is on high alert for attacks by radicalised Muslims or by home-grown militants returning from fighting in the Middle East, having raised its threat level to high and undertaken a series of high-profile raids in major cities.< eod>< sod > Police close a street where a cafe is being used to hold hostages in the central business district of Sydney Â  John Key, the New Zealand Prime Minister, is one of the world leaders to have sent messages of support to Mr Abbott.< eod>