MEXICO CITY (AP) — A popular dog run in a picturesque Mexico City park remained closed Tuesday following reported cases of dog poisoning.

Orange tape surrounded the fenced-off dog area at Parque Mexico in the well-to-do Condesa neighborhood in the central part of the capital. Large banners hung on the fence warning of a "Red Alert" that dogs are being poisoned. The shady area where dogs usually play was empty and unusually silent.

Smaller paper signs posted throughout the park by the local government advised dog owners to keep their pets on leashes while an investigation into the poisoning continued.

Several police officers standing outside the dog run said they did not know when it would reopen. One sign posted by a Facebook group on the gate had photos of nine dogs that it said had been poisoned since Sept. 29.

Javier Hidalgo, director of the environmental and mobility department for the local government, said 12 dogs had died in veterinary clinics with symptoms that could indicate poisoning and officials received reports of six other suspicious deaths.

One of those was "Daisy," described as a "mutt of the best sort" by her owner, Caroline Owen. Owen said she and her husband were aware of reports about poisoning around Parque Mexico when they were out Friday night walking their three dogs.

She said they were vigilant and kept the dogs on leashes while limiting the walk to the park's perimeter. But at 3 a.m., they awoke to find Daisy convulsing and foaming at the mouth. The other two dogs showed no symptoms. Owen had her dead pet's body frozen and it is undergoing toxicology tests at a lab at Mexico's national university.

"It can't be a coincidence that all of a sudden there are so many ill dogs," Owen said. She said she had heard of similar cases at nearby Parque Espana as well.

Information spread rapidly on social media. The Facebook page "Cuidando Nuestros Perritos," or "Taking Care of Our Dogs," posted photos of pets and testimonials by distraught owners.

Alberto Franco Paz, who lives in the neighboring Escandon neighborhood, sat outside the dog run with his yellow Labrador retriever Jackie on Tuesday.

He said he first heard about the situation Saturday when he brought Jackie to the park and saw the signs.

But he played down the threat, saying he thought people who did not like dogs coming to the park were trying to blow it out of proportion in hopes that fewer would come. He said city officials had inspected and cleaned the dog area without finding anything. He said authorities were also reviewing footage from security cameras.

"Really I'm not certain," Paz said. "But I don't know why they would do it."

A couple dozen people walked their dogs through the park Tuesday morning, but all the animals were on leashes.

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Associated Press videojournalist Teresa DeMiguel contributed to this report.