User Config\Administrative Templates\Desktop\Hide and disable all items on the desktop
You may try this in GPO. It does not prevent, but it hides them.
"Removes icons, shortcuts, and other default and user-defined items from the desktop, including Briefcase, Recycle Bin, My Computer, and My Network Places. Removing icons and shortcuts does not prevent the user from using another method to start the programs or opening the items they represent. Also, see Items displayed in Places Bar in User Configuration\Administrative Templates\Windows Components\Common Open File Dialog to remove the Desktop icon from the Places Bar. This will help prevent users from saving data to the Desktop.
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