Story highlights The elephants were found in the remote Sinamatella area of Hwange National Park

Rangers recovered 35 tusks, and poachers escaped with three, officials say

(CNN) National park officials say 22 more elephants have been killed by cyanide in Zimbabwe, adding to a worrying poaching trend.

A source with knowledge of an investigation of the killings says 78 elephants have been poisoned in the country this month.

The elephants were found in the remote Sinamatella area of Hwange National Park on Monday, Zimbabwe national park officials say. The park received international attention in July as the site where American dentist Walter Palmer shot and killed Cecil the lion.

Officials say rangers recovered 35 tusks, and poachers escaped with three. They said the remaining elephants were too young and their tusks had not fully developed.

The recent cyanide poisonings are not the first in Zimbabwe, where the poison is common and is often stolen from gold mines. In 2013, around 300 elephants were killed with cyanide in Hwange National Park in a single incident.

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