Australian Prime Minister Malcolm Turnbull has said, Counter-terrorism police have disrupted a suspected plot to bring down an aeroplane. He was speaking after four people were arrested in raids across Sydney suburbs today. <br/><br/>Mr Turnbull said, the raids had been a major joint counter-terrorism operation. He further said, the operation is still underway. Malcolm Turnbull said, security had been increased at Sydney and other domestic and international Airport since Thursday because of the suspected plot.