ICAO Doc 4444 Section 8.11 refers to the use of radar in the provision of FIS.
It specifically says that radar 'may be used to provide identified aircraft with:
a)Information regarding any aircraft observed to be on a conflicting path with the radar identified aircraft, and suggestions or advice regarding avoiding action.'
b) Weather info.
c) Information to assist the aircraft in its navigation.' (funny, I thought the pilot or another crew member did the navigation!)
There is also an implication that Radar Advisory Service may only be provided in class F airspace (sections 8.11 and 9.1.4)