(CNN) -- Iranian authorities on Tuesday released one of three people detained along with Washington Post reporter Jason Rezaian last week, a source close to the family of the released detainee told CNN on Wednesday.
The released detainee is the husband of an Iranian-American photojournalist who remains in custody with Rezaian and his wife, according to the source. Authorities have yet to identify the photojournalist, and Iranian officials have yet to explain why the journalists were detained.
According to The Washington Post, Rezaian, 38, holds American and Iranian citizenship. He has been the paper's Tehran correspondent since 2012. His wife, Yeganeh Salehi, is an Iranian citizen who has applied for U.S. permanent residency. She is a correspondent for the UAE-based newspaper the National, The Post said.
Gholam-Hossein Esmaili, the director general of the Tehran Province Justice Department, has been quoted by Iran's official IRNA news agency as saying that a "Washington Post journalist has been detained for some questions and after technical investigations, the judiciary will provide details on the issue."
He did not specify on what grounds the correspondent, whom he did not name, was being held. Iranian security forces are vigilant about all kinds of enemy activities, Esmaili added, according to IRNA.
Rights activists and fellow journalists have condemned the arrests of the journalists and demanded their release. According to research by the Committee to Protect Journalists, there are 35 journalists in prison in Iran.
Rezaian's mother made a videotaped plea for the release of her son and daughter-in-law Tuesday.
She warned that his health would be compromised without medication for high blood pressure.
"I do not know where my son and daughter-in-law are," Rezaian's mother said in a video clip posted on the Washington Post's website. "As a mother, I am extremely worried about their well-being."
Rezaian's mother noted that her son's love for Iran "is so infectious that he has made a career out of sharing its beauty with others."
"Since he was a little boy, my son loved Iran. Jason moved to Iran to live and work full-time," she said." "I love my son and daughter, and I am proud of their commitment to journalism. I know their standards for truth and excellence in journalism guide them both professionally and personally. I humbly ask those who continue to detain my son and daughter to please release them and allow our family to be reunited and my fears for their safety to subside."
In a statement Thursday, Washington Post foreign editor Douglas Jehl said, "we are deeply troubled by this news and are concerned for the welfare of Jason, Yeganeh and two others said to have been detained with them." He described Rezaian as "an experienced, knowledgeable reporter who deserves protection and whose work merits respect."