Major western cities are tightening security on New Year's Eve on concerns over numerous terrorist attacks which have taken place in the US and Europe over the past year. <br/><br/>A heavy security presence is seen at venues of various events to celebrate the New Year. London ramped up security at a New Year's fireworks event. Britain suffered a suicide attack near a concert venue in May and a bomb was detonated on a subway in September. On Friday, security fences were set up and a helicopter hovered over the venue. <br/><br/>A police official says security personnel are keeping an eye on everything – both visible and invisible. A Christmas market was attacked in the German capital of Berlin last year when a truck drove into crowds killing 12 people. One year on, an outdoor concert and other events are planned in the city for revelers celebrating New Year. Concrete roadblocks have been placed to prevent vehicles from entering event sites. <br/><br/>In New York, an improvised pipe bomb exploded earlier this month in an underground passage near Times Square. The square is a popular gathering spot for crowds to ring in the New Year. Police have mobilized more armed officers and sniffer dogs than last year.<br/>''''''