(CNN) -- Concern is growing for the wellbeing of four journalists apparently detained in Iran this week, three of them American citizens, according to the Washington Post.
The Washington Post reported Thursday that it had received "credible reports" that its Tehran correspondent Jason Rezaian, a U.S. citizen, and his wife, Yeganeh Salehi, had been detained on Tuesday evening.
Two freelance photojournalists, both American citizens, also have been detained, according to the Washington Post. The paper said officials had not yet named the pair.
"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," Washington Post foreign editor Douglas Jehl said in a statement.
He described Rezaian as "an experienced, knowledgeable reporter who deserves protection and whose work merits respect."
The Committee to Protect Journalists said it was alarmed by the Post's report and urged Iran to release the four journalists.
"We call on Iranian authorities to immediately explain why Jason Rezaian, Yeganeh Salehi, and two other journalists have been detained, and we call for their immediate release," said Sherif Mansour, its Middle East and North Africa program coordinator.
"Iran has a dismal record with regard to its treatment of imprisoned journalists. We hold the Iranian government responsible for the safety of these four."
According to the Washington Post, Rezaian, 38, holds American and Iranian citizenship. He has been the paper's Tehran correspondent since 2012.
His wife, an Iranian citizen who has applied for U.S. permanent residency, is a correspondent for the UAE-based newspaper the National, the Washington Post said.
Thomas Erdbrink, Tehran bureau chief for The New York Times, said via Twitter, "I strongly condemn the arrest of my friend and colleague @jrezaian and his wife @YeganehSalehi, and two photographers, also friends."
According to CPJ research, there are 35 journalists in prison in Iran.
The organization also highlights past instances in which Iran has detained international journalists, including the case of U.S. freelancer Roxana Saberi.