The ivory stockpile was pulverised by an industrial rock crusher at a US Fish and Wildlife Service refuge near Denver, Colorado yesterday.
The move was "a clear message that the nation will not tolerate wildlife crime that threatens to wipe out the African elephant and a host of other species around the globe," the FWS said in a statement.
Witnesses to the event included representatives of African nations and top conservationists from around the globe.
"We encourage other nations to join us in destroying confiscated ivory stockpiles and taking other actions to combat wildlife crime."
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The Philippines, Kenya and Gabon have already destroyed their stockpiles of ivory tusks and trinkets.
The US stockpile was accumulated over the course of 25 years, and was seized during undercover investigations of organised smuggling operations or confiscated at the border.
The FWS said most of the ivory, prior to being seized, was headed for illegal sale in the United States or overseas.
The multimillion dollar illegal ivory trade has driven the loss of three-quarters of all African forest elephants in the past decade, according to the Wildlife Conservation Society.
"To end the elephant poaching crisis, we know that we must take a three-pronged approach: stop the killing, stop the trafficking, stop the demand," said WCS president Cristian Samper.
The US stockpile destruction "demonstrates its own commitment to eliminating the market for illegal ivory," he said, adding that the United States could do more, such as establish a moratorium on all ivory sales within its borders.