Washington (CNN) President Donald Trump's move late Friday night to postpone a decision to allow the import of elephant hunting trophies from two African countries came as a surprise not only to interest groups, but also the US Fish and Wildlife Service employees who oversaw the proposed change in policy, a source with knowledge of the agency's process told CNN.

Agency employees responsible for recommending the change found out that it had been placed under review at the same time the public did: when the President tweeted out his decision, the source said.

Trump tweeted that he was putting the "big game trophy decision on hold until such time as I review all conservation facts," adding that the issue had been under study for years.

Put big game trophy decision on hold until such time as I review all conservation facts. Under study for years. Will update soon with Secretary Zinke. Thank you!

Trump tweeted on the issue again Sunday night, saying he would announce a decision "next week," but he would "be very hard pressed to change my mind that this horror show in any way helps conservation of Elephants or any other animal."

Big-game trophy decision will be announced next week but will be very hard pressed to change my mind that this horror show in any way helps conservation of Elephants or any other animal.

The Fish and Wildlife Service had reviewed the restrictions on the import of elephant trophies from Zimbabwe and Zambia for more thana year, as required by the Endangered Species Act , the source with knowledge of the agency's process said.

"There is a fair amount of work that goes into it," the source said. "There is a fairly comprehensive process that the state has to go through, and then biologists have to verify that."

The review process included visits to non-governmental organizations, the consideration of elephant population counts and the country's poaching management, the source said.

The source called Trump's decision to halt the policy change an "uncharted situation," saying it was the first time a president had intervened in an agency finding under the Endangered Species Act.

The President's statement Friday came just hours after White House press secretary Sarah Huckabee Sanders defended the Fish and Wildlife Service move, telling reporters that "career officials" were responsible for the proposed policy change.

Interior Secretary Ryan Zinke tweeted a statement Friday evening after Trump's tweet.

"President Trump and I have talked and both believe that conservation and healthy herds are critical," he said. "As a result, in a manner compliant with all applicable laws, rules and regulations, this issuing of permits is being put on hold as the decision is being reviewed."

The White House and Department of Interior did not respond to CNN's requests for comment about the reason for the reversal and what a further review by the administration would entail. The Fish and Wildlife Service referred CNN to Zinke's statement.

The Fish and Wildlife Service's decision to allow elephant trophy imports from Zimbabwe and Zambia was published in the Federal Register Friday.

A temporary victory?

Wayne Pacelle, CEO of the Humane Society, a national animal protection group, viewed Trump's tweet as a tentative victory.

"We're very pleased that he has intervened, and at the very least put a pause on a misguided and inhumane policy. And we are urging him to make it permanent," Pacelle told CNN. "I wouldn't say that we have high hopes. I would say that we are hopeful and that the American public is very united in opposing the trophy hunting of African elephants and African lions. And if he's attentive to Republicans and independents and Democrats alike, then he'll make the policy permanent."

On Saturday morning, Trump retweeted the Twitter posts of former Fox News anchor Greta Van Susteren and British journalist Piers Morgan , who thanked him for his move.

Sportsman's groups, however, said they view Trump's pause as only temporary.

"The way we see it, the President hasn't reversed anything. He's taking his time to make sure the decision that [Zinke] made is right," said Paul Babaz, president of Safari Club International, "We're sure the President will move ahead with the decision."

Babaz added that he believed the halt is a response to public outrage over the initial plan to lift the import restrictions, something he called "a publicity stunt."

"Honestly, we have the science on our side," Babaz said. "The money generated from hunting is in the millions and millions of dollars, and that supports programs worldwide."

Others said they see the President's decision as a stall tactic in the face of bad optics, in that the Fish and Wildlife Service finding came down within hours of a political coup in Zimbabwe.

Trump's move doesn't mean the administration is backing off its push to expand hunting rights nationally and internationally, sources said.

According to one source involved in the hunting conservation community who spoke to the President's son, Donald Trump Jr., during the 2016 campaign, members of the Trump family wanted to change Fish and Wildlife Service regulations on big-game hunting.

"I know it was a priority for Don Jr. early on, during the campaign," the source said. "I remember him mentioning it. They were frustrated."

Donald Trump Jr. and his younger brother, Eric, are both big-game hunters. Photos posted in 2012 by the website Gothamist show Donald Jr. holding an elephant tail. The website says the photos were from a 2011 hunt in Zimbabwe. Donald Jr. is also an active member of the Boone and Crocket Club, and helped with the search for Interior secretary.