Four reporters, three of them Americans, working out of Iran were reportedly detained in Tehran on Tuesday, but it is still unclear who took them and why.

U.S. officials and the Washington Post reported Thursday that Jason Rezaian, the newspaper's correspondent in Iran, and his wife, Yeganeh Salehi, were apprehended along with two other American journalists, who have not been identified.

"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," Washington Post foreign editor Douglas Jehl said in a statement.

Jehl added that 38-year-old Rezaian, who has worked with The Post in Tehran since 2012, "is an experience, knowledgeable reporter who deserves protection and whose work merits respect."

Rezaian has citizenship in both America and Iran. Rezaian received permission from the Iranian government to work for The Post in 2012 having been a reporter in Iran since 2008 and accredited to work for the San Francisco Chronicle as well.

Yeganeh, an Iranian who applied for U.S. permanent residency, is a reporter for the United Arab Emirates' newspaper, the National. The other two detainees are freelance photojournalists.

State Department spokeswoman Marie Harf said American officials have been notified about the three detained Americans and added that their "highest priority is the safety and welfare of the U.S. citizens abroad."

Hamid Babaei, a spokesman for the Iranian mission at the United Nations, said Iranian officials are currently investigating the incident.

"We will inform you as soon as we receive any news," Babaei said in an e-mailed statement.

According to CNN, Gholam-Hossein Esmaili, the director general of the Tehran Province Justice Department, reportedly told Iran's official IRNA news agency that a "Washington Post journalist has been detained for some questions and after technical investigations, the judiciary will provide details on the issue."

Sherif Mansour, the Committee to Protect Journalists' Middle East and North Africa program coordinator, demanded that Iranian authorities promptly release the four reporters.

"We call on Iranian authorities to immediately explain why Jason Rezaian, Yaganeh Salehi, and two other journalists have been detained, and we call for their immediate release," Mansour said in a statement.