WASHINGTON (Reuters) - Conservation groups sued the U.S. government on Monday over a plan to allow hunters to bring home elephant and lion trophies from Zimbabwe, following changing statements about the possible move by President Donald Trump’s administration.

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The lawsuit in federal court in Washington was the latest move in a saga that began last week when a trophy hunting group said at a conference in Africa that the White House was ready to overturn a rule banning the import of elephant trophies, sparking a surge of criticism from wildlife advocates.

The Center for Biological Diversity and the Natural Resources Defense Council said in a statement that their lawsuit intended to resolve “contradictory announcements” by the Republican administration about trophy imports of the at-risk species.

The Fish and Wildlife Service on Wednesday said it had concluded that Zimbabwe and Zambia had developed conservation plans that would allow sustainable hunting of the endangered species, an announcement that came the same week that Zimbabwe was rocked by a coup. A proposal published on Friday would have allowed both elephant and lion trophies shot in Zimbabwe, but not Zambia, to be imported into the United States.

“These two final agency actions are arbitrary and capricious, as the conclusions that trophy hunting of elephants and lions in Zimbabwe enhances the survival of the species are not supported by the evidence,” the conservation groups said in their 34-page lawsuit on Monday.

The lawsuit asked a judge to rule the move illegal and named as defendants Interior Secretary Ryan Zinke and the Fish and Wildlife Service. The Interior Department referred queries about the lawsuit to the Justice Department, which did not immediately respond to a request for comment.

Following the release of the proposed Zimbabwe rules, the White House said it had made no decision to allow trophy imports.

“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,” Trump said on Twitter on Sunday.

Africa’s elephant population plunged by about a fifth between 2006 and 2015 because of increased poaching for ivory, the International Union for Conservation of Nature said last year.

Wildlife activists argue that corruption is endemic in impoverished Zimbabwe, and that money generated by big game hunting and meant for conservation has been diverted to crooks and poachers.