Scientists and environmentalists are extremely concerned over the mysterious and unexpected deaths of 120,000 endangered Saiga antelopes over the last two weeks in Kazakhstan and how it affects the future of the threatened species.

More than a third of the total population of the Saiga antelopes has died across central Kazakhstan in what the United Nations Environment Programme has referred to as a "catastrophic collapse" and a "a major blow for conservation efforts" of the protected antelope species, Mashable reported.

While experts are still trying to figure out the exact cause of the mass deaths, a preliminary analysis suggests that a combination of biological and environmental factors could be at play.

Biologist EJ Milner-Gulland suggests that the cause of these deaths could be a rapidly-spreading deadly disease, according to The Empire State Tribune. The Convention on the Conservation of Migratory Species of Wild Animals (CMS), a U.N. treaty, believes that two forms of bacteria, namely Pasteurella and Clostridia, may have contributed to the deaths. However, this theory fails to solve the mystery, since these bacteria only harm animals with already weak immune systems.

"[The bacteria] are not the fundamental cause of the die-off....There has got to be something else that is weakening and stressing the immune systems of these animals, and it's got to be very serious because we're seeing 100 per cent mortality," said Aline Kühl-Stenzel, the terrestrial species coordinator at the CMS, the Toronto Star reported.

Kühl-Stenzel added that over 500 people have flown down to Kazakhstan to take samples and perform autopsies on the antelopes. These people will also bury the remains in order to prevent further deaths.