Preliminary tests to explain the reason for hundreds of mysterious elephant deaths in Botswana point to a naturally occurring toxin as a probable cause, a senior wildlife official told Reuters.

It was highly unlikely that an infectious disease was behind the shocking deaths of at least 281 elephants, added Cyril Taolo, acting director of the Department of Wildlife and National Parks.

Officials had been struggling to establish the cause of death more than two months after the first carcasses were spotted in the Okavango Panhandle region.

Initial investigations appeared to rule out common causes like poaching and anthrax.

"We have received more test results from other countries including the United States, and so far the results show that it's highly unlikely that the cause could be an infectious pathogen,”Taolo said.

"Our main attention ... is now on investigating broader environmental factors such as naturally produced toxins from bacteria that are found in the environment, such as water bodies.”

The government has sent samples to laboratories in Botswana, South Africa, Zimbabwe and the United States for tests.

As of last week it had received results from bacterial detection and toxicology tests in Botswana, histopathology tests in South Africa, and bacterial detection and histopathology tests in Zimbabwe.

Taolo said toxicology results were expected from South Africa soon.

"It's a game of elimination where we start testing the most common causes and then move on to the less common ones. We then have to verify and corroborate these results from different laboratory tests. We are hoping to provide a more concrete update tomorrow,”he said.

(With input from agencies)