A heavily armed police officer walks near Lindt cafe, where hostages are being held,in Martin Place in central Sydney December 15, 2014. Australian police locked down the centre of the country's biggest city on Monday after an armed assailant walked into a downtown Sydney cafe, took hostages and forced them to display an Islamic flag, igniting fears of a jihadist attack. Police said they knew of one armed assailant involved in the incident at the Lindt chocolate cafe in the heart of Sydney's financial district, but there could be more. REUTERS/David Gray (AUSTRALIA - Tags: CRIME LAW)