why can't FCPX able to import AVCHD (MTS) files from my Panasonic camcorder?

I have just changed over to a MAC system from a PC Windows 7 pro system and although I had no problems in downloading the AVCHD files into the PC Windows 7, using my iMac and fcp X the system just does not recognise anything but still images off my SDHC card. I would like to know whether it's the OS X 10.68 or fcpX that is responsible for this non recognithion of the AVCHD (MTS) files produced by the Panasonic HDC-SD900 model.