"The grave charges against Jason that Iran has now disclosed could not be more ludicrous," the newspaper's executive editor Martin Baron said after a lawyer for Rezaian revealed he would face trial on several charges.
"It is absurd and despicable to assert, as Iran's judiciary is now claiming, that Jason's work first as a freelance reporter and then as The Post's Tehran correspondent amounted to espionage."
Rezaian, a 39-year-old dual American-Iranian citizen, was detained in Tehran on July 22 last year, along with his Iranian wife who was later released on bail.
Ahsan said her client was accused of espionage, collaboration with hostile governments, gathering classified information and disseminating propaganda against the Islamic Republic of Iran.
Baron called for Rezaian to be able to add lawyers of his own choosing to his defense team, and said that if the trial were to be conducted fairly, the charges would be shown to be empty.
"The world will be watching," Baron said, adding that a just trial could only result in Rezaian's "exoneration and immediate release.