Paris CNN  — 

Three dogs have died from a suspected poisoning at a canine racing event in southern France, according to the local prosecutor.

Police were called to the French Canicross championships in the Gard region on Sunday morning, where they found three dead dogs and another that was seriously ill, according to a statement Monday from the Nimes prosecutor, Cecile Gensac.

She said the animals suffered a “sudden illness” at the race, where dogs are harnessed to an athlete in a form of cross-country running.

Initial investigations revealed that the three dogs had eaten meatballs at the event site, falling ill about 15 minutes later, Gensac said. The fourth dog had only licked one of the meatballs, it emerged.

Black pellets were found inside the meatballs, which are currently being analyzed, according to the prosecutor. More meatballs were found in a search of the area.

“The veterinarians present as part of the supervision of the race immediately mentioned a possibility of poisoning,” the prosecutor’s statement said.

An investigation has been opened into animal cruelty, Gensac said, which carries a possible sentence of five years imprisonment and a fine of 75,000 euros (around $80,400.)

The event’s second day was canceled, according to a Facebook post by the organizers, the Federation of Canine Sports and Hobbies. Organizers blamed an unknown person, or people, for putting “poisoned meatballs on the site,” adding they had filed an official report with police.

A similar report has been filed by the mayor of the town of Vauvert, the mayor’s office told CNN, adding that access to the area where the event was staged has been restricted in case of further poisonous substances.

“This weekend a particularly odious act struck our sport,” Yvon Lasbleiz, president of the Federation of Canine Sports and Hobbies, said in a post on Facebook Monday.

Addressing the three dead dogs, he said: “Oslo, Palma and Opale, your masters have lost an unconditional love.”

The surviving dog, Togo, was recovering well as of Monday, the federation said on Facebook.

“He can walk even with some little spasms in his movements, but he seems to have pulled through,” the federation said, thanking the event’s veterinarians for their efforts.