The Super 2000 World Rally Championship leaders were competing in a Peugeot 207 S2000 and were in sixth overall on the asphalt event when the crash occurred.
Medical crews reached the accident scene within minutes but Roberts sadly died from his injuries. Breen was unhurt in the accident but was treated at the scene for shock.
Following the accident, several tributes were paid to Roberts on Twitter.
Mikko Hirvonen, who drives for the factory Citroen team in the WRC, said: “I heard the sad news from Italy. Me and Jarmo want to send our condolences and our thoughts to Gareth’s family and friends on this sad day.”
Alastair Fisher, the current leader of the WRC Academy, said: “I cannot believe what’s happened. I’m totally devastated. My thoughts are with Gareth’s family and of course Craig.”
Former WRC regular Matthew Wilson said: “I really don’t know what to say. What awful news from Targa Florio. I honestly can’t believe it. RIP Gareth.”
M-Sport, which built the Ford Fiesta S2000 Breen and Roberts were using in the SWRC, said: "Our thoughts are with Gareth's friends and family. The world of rallying has lost a true talent."
In a statement from Pirelli, whose tyres Breen and Roberts used to win the WRC Academy title, the company’s motorsport director Paul Hembery said: “Words cannot express our shock and sadness. At this difficult time we would like to convey our sincere condolences to the family, friends and fans of Gareth. We are all devastated.”