A Nov. 6, 2013, photo shows Jason Rezaian, a Washington Post reporter, at the newspaper in Washington. === (Zoeann Murphy/AP)

An Iranian judicial official confirmed Friday that The Washington Post’s correspondent in Iran is in government custody, according to a report from a state news agency, but officials shed no light on the nature of an investigation that also led to the detention of his wife and two American citizens earlier this week.

Gholam-Hossein Esmaili, the head the Justice Department in Tehran Province, was quoted by the Islamic Republic News Agency saying officials would release more information about Post correspondent Jason Rezaian’s detention “after technical investigations” are complete.

Martin Baron, The Post’s executive editor, said officials at the newspaper were “mystified” by Rezaian’s arrest and remain “profoundly concerned” for his well-being and the others in custody.

“Unfortunately, we have received no information about Jason’s whereabouts, his condition, or any allegations that might be made against him,” Baron said in a statement. “We remain hopeful that he and his wife and the other detainees will regain their freedom soon and Jason can resume the work that has earned him respect over many years.”

The arrest of Rezaian, 38, who holds American and Iranian citizenship, came as a surprise to colleagues, relatives and close observers of the bilateral relationship between Washington and Tehran, which have been negotiating a landmark deal that would bar Iran from developing an offensive nuclear program. He is the first American journalist known to have been taken into custody in Iran since 2009.

A picture made available July 25, 2014 shows the Washington Post Iranian-American journalist Jason Rezaian and his Iranian wife, Yeganeh Salehi, during a foreign ministry spokeswoman weekly press conference in Tehran in September. The Iranian judiciary has confirmed the arrest of two Iranian journalists, a photographer and her husband in Tehran. (European Pressphoto Agency)

Iranian officials have not responded substantively to repeated inquiries from The Post about Rezaian’s detention. Hamid Babaei, a spokesman for the Iranian mission at the United Nations, said Friday he is seeking information from authorities in Iran.

The U.S. State Department said it was “concerned” about reports that the four journalists had been detained but was unable to comment further because of “privacy considerations.”

The United States and Iran do not have diplomatic relations. “In general, in any case involving the detention of a U.S. citizen in Iran, we would work with our protecting power, Switzerland, to request appropriate consular services,” State Department spokeswoman Marie Harf said. Asked if the Swiss had been contacted to request contact with Rezaian and the others on behalf of the United States, Harf said, “I don’t have further details . . . that I’m able to share.”

The Post and Rezaian’s relatives have not heard from him since he and his wife, Yeganeh Salehi, were taken into custody Tuesday evening in their Tehran home.

“He hasn’t been able to contact a lawyer who would be able to communicate with us where he is located,” Ali Rezaian, Jason’s brother said Friday.

Mary Rezaian, his mother, said she is worried about whether Rezaian has access to the blood-pressure medicine he takes.

“It’s really important that he have that,” she said in a phone interview from Istanbul. “Who knows if whoever came and took him gave him time to pick that up.”

Experts on Iran said Rezaian’s detention may have been carried out on the orders of hard-line factions within the government that control the intelligence and judicial branches in an effort to undermine President Hassan Rouhani, who is seen as a reformer and has embraced warmer relations with the West.

“He was likely sacrificed in this domestic infighting between the hard-liners and Rouhani’s rest of the cabinet,” said Haleh Esfandiari, an Iranian American scholar who heads the Woodrow Wilson Center’s Middle East program and was detained in Iran in 2007.

Camelia Entekhabifard, an exiled Iranian journalist based in Dubai, said Rezaian’s detention has already had a chilling effect on journalists in Iran. Colleagues there who are normally forthcoming with her about sensitive issues are being unusually circumspect, said Entekhabifard, who left the country after she was detained in the summer of 1999.

“Already local media have limited their contacts with us and are alarmed,” Entekhabifard said. “I lived in Iran and know what these ‘midnight raids’ mean. It’s a nightmare.”

She and Esfandiari described Rezaian as a fair and conscientious reporter and said none of his recent stories has been controversial or disclosed sensitive information.

“He’s very careful,” Esfandiari said. “If you look at his articles, there is nothing in them that would compromise him.”

Rezaian, who has served as The Post’s Tehran correspondent since 2012, has written a wide variety of articles about Iranian politics, foreign policy and culture. His mother said Rezaian, who was raised in California, decided to move to his father’s homeland as an adult in large part because he felt he could offer a nuanced insight of Iran, which he felt was often vilified in the Western press.

“There was so much negativity,” Mary Rezaian said, explaining her son’s thinking. “Every time Iran was on the news, they would show hostile crowds storming the gates of the U.S. Embassy. He felt that people in the United States needed to understand that there’s more to Iran than that history.”

In a video interview made when he visited The Post’s newsroom in Washington last year for the paper’s Web site, he compared the mood in Iran following the election of Rouhani, to that in the United States following President Obama’s 2008 election.

In Iran, Rezaian said, “there are very high expectations, a lot of pressure on the common man and a very difficult road ahead. I think Iranians, especially in the lower and middle classes, are saying, ‘how can this new administration make things different, other than rhetorically?’ ”

“A big part of that is potential relations with the United States,” he said, noting a desire in both countries for “some sort of end to this standoff over Iran’s nuclear program. . . . At the end of the day there are many more issues of shared importance . . . that these two countries need to talk about.”

In recent months, Rezaian has written from Vienna about Iran’s nuclear negotiations with world powers and the effect of international sanctions inside Iran. He has chronicled the still nascent popularity of baseball in the Islamic Republic, and how its government is grappling with rising female drug addiction. Other recent articles focused on government failure to deal with “a water shortage of epic proportions,” and a parliamentary move to ban abortions and criminalize permanent forms of contraception as Iran’s birthrate has fallen.

The two other Americans detained Tuesday are a female freelance photojournalist and her husband. A relative of the woman said the family is working through contacts in Iran to secure their release. He said relatives have asked that their names not be made public.

Before Rezaian and those arrested with him, at least 10 U.S. citizens have been arrested in Iran over the past decade.