The U.K. government on Friday formally approved the extradition of WikiLeaks founder Julian Assange to the United States to face espionage charges, a decision that human rights groups condemned as a dire threat to journalism worldwide.

Assange, who has been detained in a high-security London prison since 2019, is expected to appeal the move by U.K. Home Secretary Priti Patel, whose office insisted that the publisher’s extradition to the U.S. would not be “incompatible with his human rights, including his right to a fair trial and to freedom of expression.”

But Amnesty International’s Agnes Callamard, who previously worked as a United Nations human rights expert, disagreed with Patel’s assessment, warning that “allowing Julian Assange to be extradited to the U.S. would put him at great risk and sends a chilling message to journalists the world over.”

“If the extradition proceeds, Amnesty International is extremely concerned that Assange faces a high risk of prolonged solitary confinement, which would violate the prohibition on torture or other ill treatment,” Callamard said in a statement.