How to make bootable usb from part iso files?

I am trying to make a bootable usb disk for a linux distro. The image files i downloaded is in parts like linux_dvd1of3.iso, linux_dvd2of3.iso, linux_dvd3of3.iso. I want to write these part iso files into usb to create a bootable usb disk. How can I make a bootable usb disk using these part iso files?