The lawyer for detained Washington Post journalist Jason Rezaian says her client is facing trial for espionage and three other charges including collaboration with hostile governments.

Rezaian, the newspaper's Tehran correspondent, has been in jail for nine months, but Leila Ahsan says no date has yet been set for court, adding the case against him contains no justifiable proof.

In a telephone call after meeting Rezaian, she says he is also accused of gathering classified information and disseminating propaganda against Iran.

Rezaian, 39, was detained in Tehran on July 22 last year, along with his Iranian wife who was later released on bail.