I noticed a row of 4 dust spots on some of the photos from my recent trip to Iceland I performed my sensor cleaning workflow using a blower followed by the amazingly effect Arctic Butterfly Brush and then finally a couple of 'wet' cleans using visible dust swabs. This exercise resulted in a spotless sensor with the exception of the row of 4 which stubbornly refused to go (or even change position)
After further investigation I notice that this row has been appearing in shots since I purchased the camera and therefore my conclusion is that they must be behind the sensor glass.
I have had very good experience with Fuji Service in the past and have decided to send the X-T1 back to them for repair. The spots are hardly critical but still worth getting resolved while the warranty is in place.