UPDATE 2-Four soldiers killed in helicopter crash in Istanbul - city governor

Four soldiers were killed when a military helicopter crashed in a residential neighbourhood on the Asian side of Istanbul on Monday, the governor of Turkey's biggest city said.

The helicopter went down in an area of apartment buildings, Istanbul Governor Ali Yerlikaya said. Television images showed smoke rising from the area and ambulances rushing to the scene. There were no civilian injuries or casualties, Yerlikaya told reporters, adding that the cause of the crash was not yet known. (Reporting by Ece Toksabay Editing by Dominic Evans and Gareth Jones)