The carcasses of five more elephants were discovered in Thailand downstream from a waterfall known as the "Ravine of Hell," where six other elephants plummeted to their deaths over the weekend, officials said Tuesday.

The first group of elephants was thought to have died Saturday while trying to rescue a 3-year-old calf that had slipped over the Haew Narok Waterfall in Khao Yai National Park, according to the country’s National Parks, Wildlife and Plant Conservation Department. The calf and five adult elephants were found dead near the base of the falls.

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While the ravines are known to overflow with water during the rainy season, it was not immediately clear why the elephants fell into the strong current.

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As officials investigated how the first six elephants fell to their deaths, they spotted the second group of five carcasses by drone, spokesman Sompote Maneerat said. The new victims are thought to have come from the same herd.

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When the first group was discovered over the weekend, officials also found two surviving elephants struggling on a cliff edge. Those elephants have been moved and were being monitored.

The death toll of 11 marks the highest number of elephants to die in a single incident in Khao Yai, Sompote said.

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In 1992, a herd of eight elephants died after they slipped and fell over a waterfall while trying to cross a river. In that incident, the Forestry Department was heavily criticized for not doing enough to make the park safe for elephants.

The elephant population at the park is estimated to be about 300. More than half of Thailand’s population of 7,000 Asian elephants live in captivity.

Fox News' Julia Musto and The Associated Press contributed to this report.