El Salvador has agreed to house violent US criminals and receive deportees of any nationality, officials from both countries announced Monday, in an unprecedented deal with the Trump administration that has alarmed critics and rights groups.

He also said El Salvador could take in American citizens and legal residents convicted of crimes and house them in maximum security prisons, which the state department called “an extraordinary gesture never before extended by any country”, though it was not clear if Washington would accept the offer.

It is unclear whether the Trump administration plans to send incarcerated U.S. citizens to El Salvador. Secretary of State Marco Rubio said the U.S. was “grateful” for the offer.