More than six tons of confiscated ivory have been crushed in the United States.
Thousands of items of tusks, carvings and jewellery accumulated over the past 25 years were dumped into a steel crusher at the National Wildlife Property Repository north of Denver, Colorado.
They were seized from smugglers, traders and tourists since an international embargo on the ivory trade took effect in 1989.
Elephants continue to be shot for their tusks despite the global ban.
Officials said the collection represented the killing of more than 2000 adult elephants.
Last year saw the highest number of large seizures of illegal ivory for more than two decades.
On Wednesday, US Secretary of State John Kerry announced a reward of $US1 million against members of a poaching syndicate based in Laos that slaughters elephants and rhinos for their tusks and horns.
He said profits from wildlife trafficking were being pumped into other illicit activities such as narcotics, arms and human trafficking.
