Washington Post Iranian-American journalist Jason Rezaian (R) and his Iranian wife Yeganeh Salehi, who works for the UAE newspaper National,. Both were arrested by Iranian authorities July 21st. (Stringer/EPA)

IRAN’S RELATIONS with international media have improved considerably since the election of Hassan Rouhani as president and the beginning of serious negotiations over its nuclear program. More Western journalists have been allowed to visit the country, Mr. Rouhani and Foreign Minister Mohammad Javad Zarif have given numerous interviews to Western journalists and U.S. newspapers, including The Post, have featured their op-eds. So much has the climate improved that U.S. conservatives routinely charge that U.S. media have been seduced by the new leadership.

The enhanced interchange is one reason the detention of The Post’s correspondent in Tehran, Jason Rezaian, is so unwarranted. Mr. Rezaian, a dual U.S.-Iranian citizen, and his wife, Yeganeh Salehi, who is also a journalist, were arrested at their home last Tuesday. Since then, their families and The Post have not heard from them, though an Iranian judicial official confirmed Friday that they were in government custody. Two U.S. citizens working as freelance photographers are also being held. No charges have been brought, and the detainees apparently have had no access to legal counsel. Their whereabouts are unknown.

Mr. Rezaian, who grew up in California as the son of an Iranian immigrant, went to the country in 2012 because he believed he could offer a more nuanced portrait of Iran, his mother told The Post. He has reported not just on political developments in Tehran but also on social issues, such as a water shortage, and cultural developments, including a nascent Iranian appetite for baseball. When he was arrested, he had just returned from covering the latest round of negotiations in Vienna over Iran’s nuclear program, where the two sides reported progress and agreed to a four-month extension.

In an interview last year with Post videojournalists, Mr. Rezaian said he had observed that both Iranians and Americans wanted “some sort of end to this standoff over Iran’s nuclear program” because “at the end of the day there are many more issues of shared importance . . . that these two countries need to talk about.” That pretty well sums up the argument Mr. Rouhani has advanced since his election, as well as that of President Obama since he came to office.

So why have Mr. Rezaian, Ms. Salehi and the photographers suddenly become the first American journalists detained in Iran since 2009? Post editors say they have no answers. What is known is that Mr. Rezaian, 38, suffers from high blood pressure and probably does not have access to his regular medication. In addition to endangering his health, his arrest silences a reporter who was dedicated to fairly explaining Iran to Washington readers. It also raises questions about whether Mr. Rouhani’s professed policy of “constructive engagement” is still in effect. Tehran could quickly and easily silence these doubts by unconditionally releasing Mr. Rezaian, Ms. Salehi and the other Americans.