US President Donald Trump says he is putting plans to reverse a ban on the importation of body parts from African elephants shot for sport on hold until he can "review all conservation facts".

On Thursday, the US Fish and Wildlife Service said it would allow elephant trophies in Zimbabwe and Zambia to be imported.

The agency said encouraging wealthy big-game hunters to kill the threatened species would help raise money for conservation programs.

But today Mr Trump tweeted that he was delaying the new policy, saying he would review the issue with Interior Secretary Ryan Zinke.

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The decision to reverse the ban had been quickly praised by groups that champion big-game trophy hunting.

But it drew sharp criticism from conservation groups — who argued the move would further imperil endangered species — and others on social media, who pointed out that Mr Trump's two adult sons are avid trophy hunters.

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A photo of Donald Trump Jr holding a knife and the bloody severed tail of an elephant in Zimbabwe in 2011 sparked anger among animal rights activists.

Elephant trophies are 'blood currency' for terrorists

On Friday, the Republican chairman of the House Foreign Affairs Committee, Ed Royce, urged the administration not to reverse the ban.

Mr Royce questioned the action because of concerns not only about African wildlife but US national security, citing the political upheaval in Zimbabwe, where longtime President Robert Mugabe was placed under house arrest this week by the military.

"The administration should withdraw this decision until Zimbabwe stabilises," the committee chairman said in a statement.

"Elephants and other big game in Africa are blood currency for terrorist organisations, and they are being killed at an alarming rate.

"Stopping poaching isn't just about saving the world's most majestic animals for the future — it's about our national security."

He also said he had zero confidence that the regime in Zimbabwe was "properly managing and regulating conservation programs"..

The African elephant has been classified as "threatened" under the US Endangered Species Act since 1979.

Illicit demand for elephant ivory has led to devastating losses from illegal poaching as the natural habitat available for the animals to roam has also dwindled by more than half.

As a result, the number of African elephants has shrunk from about 5 million a century ago to about 400,000.

That number continues to decline each year.

AP/ABC