Last month Osmanagic told National Geographic News that he was "100 percent convinced" that the pyramid was real.
Those claims have drawn near unanimous contempt from professional archaeologists.
Harding, an expert on Bronze Age Europe, has dismissed Osmanagic's theories as "wacky" and "absurd."
Balkan prehistory expert Curtis Runnels, an archaeologist at Boston University and editor of the Journal of Field Archaeology, joins the chorus of skeptics.
"Mr. Osmangic offers no concrete physical evidence to support his claims, despite the fact that they are fantastic," he said.
"[T]he area was in fact occupied by Upper Paleolithic hunter-gatherers with a Stone Age technology sufficient for building fires, tents, and simple hunting implements like bows and arrows."
"They were not pyramid builders."
In another recent twist, wire reports quoted Aly Abd Alla Barakat, a geologist with the Egyptian Mineral Resources Authority.
Barakat, who visited the hill at the behest of Osmanagic's team, told the Associated Press late last week, "My opinion is that this is a type of pyramid, probably a primitive pyramid."
To the AFP, he said: "The white stuff I found between the blocks could be a glue. It is very similar to that we have found in the Giza pyramids."
Critics remain unswayed, and some have questioned Barakat's expertise.
Of the alleged Bosnian pyramid, the European Association of Archaeology's Harding said, "You'd be surprised how many natural stone formations can look as if they are man-made."
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