The sudden deaths of all five meerkats at the Philadelphia Zoo this month were apparently caused by an accidental poisoning linked to a dye that is used to mark the animals, zoo officials said, but an investigation into the deaths remains ongoing.

The meerkats — named Nkosi, Lula, Nya, Kgala, and Ari — came to the zoo as a group of siblings about a decade ago. The animals are gregarious and are known for their playfulness and communal living style.

Zoo officials use dye to mark the animals as a way to differentiate them as individuals, according to Rachel Metz, the zoo’s vice president of animal well-being. She said the zoo has been using the same dye for more than three decades without incident.

1 OF 4 PEACOCKS THAT ROAMED FROM PHILADELPHIA ZOO FOUND DEAD

 A meerkat

A meerkat is shown in its enclosure at the Madrid Zoo. All five meerkats at the Philadelphia Zoo have died after being accidentally poisoned. (Marcos del Mazo/LightRocket via Getty Images)

The dye was used on the meerkats June 1, and one of them was found dead about 30 minutes later, officials said. The four others started showing signs of acute illness minutes later, so veterinary staff anesthetized them and pumped their stomachs. But three of the meerkats then died within 36 hours. The last one died Monday night after being under medical supervision for more than a week.

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Metz said the zoo is conducting a detailed investigation and noted that necropsy results are pending.