The UN training and research agency UNITAR said its satellite programme had compared images of the site taken on June 26 and again on August 27.
"We confirm the destruction of the main building, while surrounding columns seem to be less affected," UNITAR said in a statement.
The grainy images show that the famed temple, considered the second-most significant in ancient Palmyra, "has been blown to bits," spokesman Einar Bjorgo told AFP.
"It has been flattened," he said.
The destruction, which reportedly happened last Sunday, just days after Daesh fighters beheaded the 82-year-old retired chief archaeologist of Palmyra, sparked widespread outrage.
The UN has slammed the destruction of the temple as a "war crime", and the act has raised concerns for the rest of the UNESCO World Heritage site.
Famed for its well-preserved Greco-Roman ruins, Palmyra was seized from government forces in May, prompting concerns Daesh might destroy it as it has other heritage sites in parts of Syria and Iraq under its control.
Daesh published images earlier this week showing militants placing barrels and small containers, presumably containing explosives, into the temple, as well as similar containers placed on parts of its columns.
The images, which appeared to be screenshots from a video, also showed a large explosion apparently as the temple was blown up, and then a pile of rubble at its former location.